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Old 01-27-2024, 02:30 PM   #1
Fairlane514
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Default Misfire mystery

29 Tudor

Here's what I have done to chase the misfire.

Set points (.020) use NuRex wrench to set timing

New plugs Champion W18 gapped .035

Zenith carb rebuilt

Wiring all good

New condenser NAPA FA-82

Coil ohmed at 1.5 and 7500 secondary side

Alt is charging

Compression check, 60psi on all cylinders

Valve check by removing schraeder valve from compression gauge and do 10 cycles of each cylinder.......all four cylinders pumped up to 60psi each cycle without hesitation. Trying to test for a possible bad valve guide not letting valve return square to seat and cause issue.

It starts up with ease and idles but has a definite misfire that is not rhythmic. My vacuum gauge shows needle bounce down from 21 to 18 or so, randomly.

When a listen at tail pipe (new muffler) I can easily hear the misfire.

The distributor shaft is not loose or wobbly and it has the NuRex points plate and new style points/condenser.

Have not tried new coil

Fuel is fresh with some Marvel in it as well as the oil.....one quart of Marvel.

When driving really not a noticeable misfire by feel, but can hear it.
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Old 01-27-2024, 04:08 PM   #2
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Default Re: Misfire mystery

Check and make sure you are not shorted somewhere in the distributor. Is the wire from the lower plate still OK? Is there a short in the terminal box?
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Old 01-27-2024, 04:40 PM   #3
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Default Re: Misfire mystery

I went through the distributor all wires are good, reset points, filed them a little, reset timing. No change

The misfire is not consistently rhythmic, it seems more random. New wiring in terminal box seems good.

New intake/exhaust gaskets
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Old 01-27-2024, 04:43 PM   #4
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Default Re: Misfire mystery

Set timing using Les Andrews red book. Had a problem like you said, turned out that the NU REX wrench was off by a few degrees retard. When set with test light everything turned out OK. I think it has to do with modern points and NU Rex wrench. I think wrench is made ok, but some combination of new points and modern plate just did not jive in my situation.
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Old 01-27-2024, 04:44 PM   #5
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Default Re: Misfire mystery

Thinking about possible weak valve spring. May return fast enough to seal when just using starter to check compression, but at running rpm not able to perform as it should.....
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Old 01-27-2024, 04:44 PM   #6
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Ok, I will try with the light, thanks
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Old 01-27-2024, 04:51 PM   #7
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Default Re: Misfire mystery

Run it in darkness and look the distributor over, the flat plug wires to the body, coil wire to the cap. If you have an extra cap cut it down to have a good look inside.
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Old 01-27-2024, 05:10 PM   #8
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Default Re: Misfire mystery

I have a clear cap, and can see spark at each terminal at night.

Also grounded each plug strap with a screwdriver, all cylinders react the same. No dead hole with this test
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Old 01-27-2024, 06:17 PM   #9
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Default Re: Misfire mystery

Check to see if #3 spark plug strap is intermittently shorting out on the spark advance rod. With all the lights off in your garage, start it up and look for stray sparks.
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Old 01-27-2024, 06:33 PM   #10
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Default Re: Misfire mystery

Yeah , did that as well, at night all I see is sparks through the clear cap, nowhere else.

Did the Les Andrews timing with a light bulb etc... No change
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Old 01-27-2024, 06:37 PM   #11
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Default Re: Misfire mystery

I also notice (may be normal) anything more than halfway down on spark advance, it sounds like some detonation. Thats at idle, so like I said probably normal until its under load.
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Old 01-27-2024, 08:23 PM   #12
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Default Re: Misfire mystery

Clean and tighten grounds and cable connections, if you have a safety fuse replace it and, if still failing, next bypass it, check the key switch by jiggling it up, down, side to side and that it has detentes at off and on. It should not shut down if not fully in the off detent. Tighten all connections behind the panel and in the terminal box, also at the coil.

Push the coil wire up at the coil and down at the distributor. You've had them apart.

If you have the the spark tester that Nurex sells, it can show you a misfire in the secondary circuit.

Grab the upper distributor plate by the spark lever and try to move it fore and aft etc. but in the plane parallel with the engine head. The center hole may be worn allowing the points to move around. Look at the points rub block / cam follower and make certain that it is not too worn allowing the occasional spark to jump to the cam.

Check that the condenser lower plate wires at the side of the upper plate are not sticking up too high and allowing a spark from the underside of the rotor to the connections. This would likely be consistent on #3 cylinder.

Look closely at the contact surfaces of the points. If they are pitted, burned or have high spots, suspect a condenser.

There are some voltage tests in chapter 2, pages ~30-32?? of the blue, Les Andrews, "Troubleshooting and Diagnosis" book that will identify faulty, high resistance connections, both power side and grounds.

That's all I can think of quickly.
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Old 01-27-2024, 08:35 PM   #13
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Default Re: Misfire mystery

Thanks Rob, I went through the distributor, took it apart checked all suggested areas, they look good and almost new. No wobble in shaft, points look good, new condenser. Center is tight when moving the plate. Rub block looks good

Key switch may be in need of a closer look. I do notice when turning the ignition off, it seems to cut off very quickly maybe before the detent as you suggested.

Grounds from battery are good....one to the body at original location and another from there to the transmission with heavy 4 gauge wire. Both clean and tight

I do have a safety fuse wired to power cable at starter.

Mine is no longer pop out ignition switch.

I dont have the blue book by Les
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Old 01-27-2024, 11:59 PM   #14
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Default Re: Misfire mystery

Quote:
Originally Posted by Fairlane514 View Post
Key switch may be in need of a closer look. I do notice when turning the ignition off, it seems to cut off very quickly maybe before the detent as you suggested.
I've had an aftermarket switch cause trouble. It was one with the terminals at the back protruding towards the radiator and parallel to each other. The terminals and the end of the switch are swaged n and had become lose. I use a light clamp to push them back into place, then pushed some epoxy putty in around the edge of the swaged end, left it clamped while the putty set and there has been no trouble since.
BTW, how long is it since you replaced the spark plugs?
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Old 01-28-2024, 03:15 AM   #15
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Default Re: Misfire mystery

Try a different distributor cap to rule out internal arcing, this can cause a random misfire without any visual arcing.
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Old 01-28-2024, 06:32 AM   #16
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Default Re: Misfire mystery

Also check for a vacuum leak at the carburetor or intake manifold.
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Old 01-28-2024, 09:30 AM   #17
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Default Re: Misfire mystery

There is a SNEAKEY SHORT CIRCUIT in the rotor that cannot be seen. This could be the cause. Also try a different distributor body.These slides might help you.
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Old 01-28-2024, 09:46 AM   #18
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Default Re: Misfire mystery

New plugs Champion W18

I have a "modern style" distributor cap and wires I could try.

No vacuum leak, brand new intake/exhaust gaskets

Im also going to check out the ignition switch and the terminal box. Heard of the bolts touching the firewall......

Should have some results today

My current distributor body and cap are new
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Old 01-28-2024, 10:23 AM   #19
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Default Re: Misfire mystery

Fairlane,


Thank you for the direct and clear responses to all the suggestions posted.
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Old 01-28-2024, 02:02 PM   #20
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Default Re: Misfire mystery

When checking for manifold leaks, if your wiper is vacuum, plug the line. Check around the throttle lever at the throttle plate, too.
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Old 01-28-2024, 02:07 PM   #21
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Default Re: Misfire mystery

Put on the original (came with the car) "new" modern style distributor cap,rotor and wires. No change

Checked for ground continuity on the main studs from the terminal box. I had ground on both studs with battery connected, no continuity when battery ground disconnected.

Cant do much with the ignition switch, but it does seem to work, wiggled it while running, it never shut off.

Bypassed the main 30amp fuse .....no change, but may have gotten a little worse to be honest.

I did replace the ammeter when I first got the car, but it did have a misfire then as well.
I wired the new ammeter the same as the original and it read backwards , so I switched the wires. I also have the dash light wired in with the ammeter if that matters.

Coil looks to be wired correctly....red wire passenger side to the + on coil, black wire to - on the other primary stud drivers side.
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Old 01-28-2024, 02:16 PM   #22
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Default Re: Misfire mystery

Also.....with battery ground disconnected, I do have continuity between the main studs on the terminal box
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Old 01-28-2024, 03:00 PM   #23
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Default Re: Misfire mystery

No vacuum operated wipers, only manual.

Sprayed brake clean at manifold to head and carb to manifold.....no leaks (new gaskets everywhere)

I have a vacuum port, but my gauge is plugged in and shows the needle dip with each misfire.....which is random. not rhythmic.

My wiring is....

Drivers side of terminal box stud...Yellow/black tracer and coil black wire to neg side of coil.

Passenger side terminal box stud.....yellow wire

Ammeter (if looking at gauge installed in cluster and screwed to dash) .....passenger side yellow/black tracer. Drivers side.....yellow

From ignition switch one side to distributor cable, the other straight to positive side of coil (red wire)

Alternator (6 volt pos ground) has yellow/black tracer to drivers side of terminal box.

Only variables I have not switched out.......coil and carburetor. Coil ohmed at 1.5 primary, 7500 secondary

Carb is Zenith 1 which I rebuilt, checked jets for proper sizing and shape. float level good as well. I did not buy the Renner's jets...
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Old 01-28-2024, 03:07 PM   #24
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Possibly a valve is hanging up intermittently?
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Old 01-28-2024, 03:42 PM   #25
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Yeah, thought about that. I did a test with my compression gauge. I took the schreader (sp) valve out and then did 10 cycles of each cylinder watching the needle.

All four cylinders bumped the needle to 60psi every cycle quick and sharp. But thats only turning it at the speed of the starter, maybe at faster cycles one or two hangs up.
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Old 01-28-2024, 03:59 PM   #26
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I know you said manual wipers, but does your intake have a plug in that port? I'm thinking remove the plus and idle it it. Tubing, and a dose of marvel mystery oil. If a valve is hanging up that might clear it.
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Old 01-28-2024, 04:01 PM   #27
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I have a video of my vacuum gauge while running, but Im not very good with computers and cant get it to upload
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Old 01-28-2024, 04:03 PM   #28
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Gene yes, I can try that, I have my gauge plugged into the intake, so I do have barbed port
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Old 01-28-2024, 07:33 PM   #29
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Ok,

Borrowed a carburetor and a new distributor cam.

Did each change one at a time, no difference....

Wasnt able to try the MMO in the intake vacuum port yet
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Old 01-28-2024, 09:10 PM   #30
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Quote:
Originally Posted by Fairlane514 View Post
Coil looks to be wired correctly....red wire passenger side to the + on coil, black wire to - on the other primary stud drivers side.
You can't confirm correct coil wiring with above description.

You need to confirm that the black wire on the - post of the coil connects to one of the screw posts inside the black terminal box. That is the power feed to the coil.

The red wire connected to the + post of the coil needs to go to one of the connection screws on the key switch. The other connection screw on the key switch needs to connect to the wire that goes down to the distributor, to the points.

Just seeing a wire color on the coil is not enough. You have to know what's connected on the other end of those wires.
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Old 01-28-2024, 10:15 PM   #31
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Yes red wire is coming from the ignition switch to the + side of coil
The other side of the ignition switch goes to the armored wire to distributor.

Black wire to - side of coil goes to terminal box stud on drivers side which also has yellow/black tracer wire attached. Yellow/black is also attached to alternator.

Pretty sure I mentioned this in post #23
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Old 01-29-2024, 12:42 AM   #32
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Default Re: Misfire mystery

OK, then try to adjust idle mixture a bit leaner. Make very small adjustments on a fully warmed up engine.
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Old 01-29-2024, 08:55 AM   #33
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Default Re: Misfire mystery

In post 13 you said "no longer have pop out switch". Did you install new switch? If so the new switches are longer than original and just barely contact the gas tank. I had this problem, the cure was to glue an old inner tube to the gas tank. The inner tube insulated the switch from the tank. I found the problem by pushing on the dash panel while the engine was running. Good luck .
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Old 01-29-2024, 09:15 AM   #34
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It does have an aftermarket switch......I have run it with the dash hanging down and not mounted.....no change.

I have adjusted my idle mixture screw according to my vacuum gauge and about 1/4 turn either side of the most vacuum achieved, no difference.

I think at this point, it must be a sticky valve or two......I have Marvel in the fuel and oil, im just going to drive it a little bit hard and see if it finally frees up.
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Old 01-29-2024, 12:58 PM   #35
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Default Re: Misfire mystery

Positive or negative ground? Check coil polarity to be sure that the + terminal is actually connected to +
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Old 01-29-2024, 01:25 PM   #36
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One quart of MMO is either a mis-print or way too much!
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Old 01-29-2024, 02:12 PM   #37
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Positive ground as original....to the body and then again to transmission. Coil wired correctly.

One quart of MMO in the oil, about 2 ounces in 1/2 tank of fuel
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Old 01-29-2024, 04:12 PM   #38
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It does have an aftermarket switch......I have run it with the dash hanging down and not mounted.....no change.

I have adjusted my idle mixture screw according to my vacuum gauge and about 1/4 turn either side of the most vacuum achieved, no difference.

I think at this point, it must be a sticky valve or two......I have Marvel in the fuel and oil, im just going to drive it a little bit hard and see if it finally frees up.
Sounds like a good plan ! Enjoy the drive !
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Old 01-29-2024, 04:56 PM   #39
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Keep us posted on progress!
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Old 01-29-2024, 06:10 PM   #40
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Drove it some today, to a fellow Model A owner about 10 miles away.

It seems to have plenty of power and cruises well, I dont really notice the misfire when driving and underload. I come to a stop, it stays running. A little clutch chatter on take off (another issue to address), but upshifts fine.

No real difference as of yet.....

The other owner does have an aluminum head he wants to sell, I will post that separately. Cant ID it....Has the letter R with two circles around it cast right near the distributor hole.
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Old 01-31-2024, 06:48 AM   #41
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Default Re: Misfire mystery

Before you tear into the valves I would try a new condenser.
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Old 01-31-2024, 09:34 AM   #42
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I did that already, Echlin FA-82......

Not say its not a faulty new one.....it runs the same with the old condenser versus the new one.

Its the modern style points and condenser with the NuRex plate etc
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Old 01-31-2024, 09:50 AM   #43
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Quote:
Originally Posted by Fairlane514 View Post
Drove it some today, to a fellow Model A owner about 10 miles away.

It seems to have plenty of power and cruises well, I dont really notice the misfire when driving and underload. I come to a stop, it stays running. A little clutch chatter on take off (another issue to address), but upshifts fine.

No real difference as of yet.....

The other owner does have an aluminum head he wants to sell, I will post that separately. Cant ID it....Has the letter R with two circles around it cast right near the distributor hole.
The "R" cast into the head, possible it could be a Ricardo head?
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Old 01-31-2024, 09:53 AM   #44
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I have no clue, research doesnt come up with much.

Riley maybe? May be a stock replacement head, but why aluminum....
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Old 01-31-2024, 09:55 AM   #45
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https://www.fordbarn.com/forum/attac...1&d=1706712884
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Old 01-31-2024, 10:17 AM   #46
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Man that head needs a good glass bead blasting ,it’s probably a Riley !?
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Old 01-31-2024, 10:20 AM   #47
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If you can feel the misfire from the driver's seat, watch the ammeter for any slight twitch. As described, your car is wired correctly as per the 1929, Nov. service bulletin. A steady or intermittent, unintended ground between the pos + post of your coil and the ignition points likely would affect the reading at the ammeter. With the engine not running, a steady, unintended ground should show a small neg - reading. The primary windings of the coil prevent the safety fuse from blowing. I've not yet experienced such an issue myself.

I'm not certain whether or not you could see the single intermittent misfire, but if you can feel it from the seat and see a coinciding, small twitch in the ammeter, it would indicate the location of the problem.

It is easy to bypass the switch and the heavy cable to the distributor with the modern upper plate installed. Unhook the red pos + wire at the coil and the wire from the lower plate at the side of the upper plate. Insulate the ends of the wires removed. Run the jumper wire from the coil pos + to the side of the upper plate. Use minimum of 16 gauge wire.

Pull the safety fuse to shutdown the engine.
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Old 01-31-2024, 10:39 AM   #48
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Default Re: Misfire mystery

Check the rivets and the insulators on the lower (and upper??) plates for tightness. A club member's distributor was recently found to have loose rivets, which allowed an intermittent issue.

Marshal Daut posted some time ago that he had, on a couple occasions, found that a reproduction terminal box had it's studs loosen. This allowed the screw heads of the studs to get close enough to the firewall to jump a spark. The heads of the terminal box studs of an original terminal box are covered. The repro's are not, but they should be.
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Old 01-31-2024, 04:07 PM   #49
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Default Re: Misfire mystery

I did check for continuity between the terminal box studs and the firewall, none found.

When I had the distributor apart and did check the rivets, they are tight.....all that stuff looks pretty new. The shaft is solid without wobble and very little end play as well.

I can try the bypass test.

I have tried posting the video of my vacuum gauge, but it states "no security button" or something to that effect.
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Old 01-31-2024, 07:36 PM   #50
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Default Re: Misfire mystery

Well......nothing simple so far, tried what has been suggested, which I really appreciate.

I think I will drive it more and see if it clears up.

I do want to upgrade to a high compression head, so when its apart I will check valve guides, springs etc...
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Old 02-01-2024, 01:45 PM   #51
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Default Re: Misfire mystery

Quote:
Originally Posted by Fairlane514 View Post
I think I will drive it more and see if it clears up.
That may be what it needs, some good serious running.
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Old 02-01-2024, 09:03 PM   #52
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Thinking out loud here....

Worn distributor gear?
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Old 02-04-2024, 01:26 PM   #53
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Default Re: Misfire mystery

'Sounds as if you've covered most bases, but still no luck finding the source of the misfire? It's there someplace. These cars didn't leave the factory with misfires. You'll find it. I'm leaning towards a weak or broken valve spring, too, since you have eliminated most electrical and carburetor-related misfire causes. TBD...
I didn't see it mentioned, but do you have a water temperature or oil pressure gauge with a light bulb for gauge face illumination? And if so, where does it get its power? I know this sounds weird, but if you do have one or both of these aftermarket gauges, disconnect the wire for the light from its power source. Why? Years ago I chased a misfire in a 1931 Coupe that I had rebuilt for a doctor friend a decade before in Phoenix. He had died in the meantime and his car showed up locally for sale. My friend had added a water temperature gauge or oil pressure gauge (I don't recall which) since I had restored the car. The car showed up with a definite miss under power demands, but the engine idled nicely. I jumped through all the hoops you have, but still couldn't find the source of the misfire.
Eventually, I disconnected the gauge's light bulb wire to completely remove the instrument panel to check for shorts. The gauge was located in a bracket beneath the panel, so it went with the now-removed panel. When I re-installed the instrument panel after finding nothing wrong with the connections behind it, I neglected to hook up the gauge's light wire. Starting the engine and test driving it for the millionth time - behold! The misfire was gone!!! I noticed the gauge's wire dangling beneath the gas tank, so I reconnected it to the terminal box's hot stud where it had been. Guess what! The misfire was back! Disconnecting the wire again, the misfire went away. I deduced that for some reason, that light socket was causing the engine to misfire by interfering with the ignition system via the terminal box stud. Maybe that's what is causing your misfire. If you don't have an auxiliary water temperature or oil pressure gauge with a light bulb, ignore what I just spent the last 10 minutes typing. But maybe this information will help someone else with a similar problem.
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Old 02-04-2024, 04:05 PM   #54
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Default Re: Misfire mystery

Quote:
Originally Posted by Marshall V. Daut View Post
'Sounds as if you've covered most bases, but still no luck finding the source of the misfire? It's there someplace. These cars didn't leave the factory with misfires. You'll find it. I'm leaning towards a weak or broken valve spring, too, since you have eliminated most electrical and carburettor-related misfire causes. TBD...
I didn't see it mentioned, but do you have a water temperature or oil pressure gauge with a light bulb for gauge face illumination? And if so, where does it get its power? I know this sounds weird, but if you do have one or both of these aftermarket gauges, disconnect the wire for the light from its power source. Why? Years ago I chased a misfire in a 1931 Coupe that I had rebuilt for a doctor friend a decade before in Phoenix. He had died in the meantime and his car showed up locally for sale. My friend had added a water temperature gauge or oil pressure gauge (I don't recall which) since I had restored the car. The car showed up with a definite miss under power demands, but the engine idled nicely. I jumped through all the hoops you have, but still couldn't find the source of the misfire.
Eventually, I disconnected the gauge's light bulb wire to completely remove the instrument panel to check for shorts. The gauge was located in a bracket beneath the panel, so it went with the now-removed panel. When I re-installed the instrument panel after finding nothing wrong with the connections behind it, I neglected to hook up the gauge's light wire. Starting the engine and test driving it for the millionth time - behold! The misfire was gone!!! I noticed the gauge's wire dangling beneath the gas tank, so I reconnected it to the terminal box's hot stud where it had been. Guess what! The misfire was back! Disconnecting the wire again, the misfire went away. I deduced that for some reason, that light socket was causing the engine to misfire by interfering with the ignition system via the terminal box stud. Maybe that's what is causing your misfire. If you don't have an auxiliary water temperature or oil pressure gauge with a light bulb, ignore what I just spent the last 10 minutes typing. But maybe this information will help someone else with a similar problem.
Marshall
Wow, I don't think anybody would have found that one without the sort of luck you had. I am chasing a miss in a friend's car at the moment and your finding might help. He has a temperature gauge with the light permanently on. I don't know yet where it is connected but I bet it is behind the instrument panel. I plan on connecting it to the tail light circuit so that it is only on when the lights are on and on regardless of high or low beam or parking lights.
FWIW, The symptoms on my friend's engine would indicate a vacuum leak. I found and fixed one but the miss was only reduced, not fixed. At some point, someone has fitted a PCV valve and a hose from the oil filler cap to the inlet manifold. Disconnecting that cured the problem but allowed oil to literally pour out of the back of the motor. Next step is to drop the sump and check out the rear bearing/oil slinger etc area. I suspect something is so wrong there that air is entering the motor, travelling through the crank case until it is sucked into the manifold, causing it to run lean.
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Old 02-04-2024, 09:22 PM   #55
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Default Re: Misfire mystery

No , I dont have any gauges.....Im going to drive it some more, and then pull the valve cover when I get some time from my other 4 projects.

Thanks to everyone for the help.

I will post what I find
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Old 02-25-2024, 08:55 PM   #56
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Got the head off today. Cylinders look pretty good, minimal ridge at top, barely feel it.

Valves need lapping, exhaust have baked on "sand" like coating.

New springs are shorter and thicker wire by about .015 thousandths. Look to measure 50 pounds pressure at 2.250 length. Old springs were 10 pounds less at same length.
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Old 02-26-2024, 08:14 AM   #57
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Default Re: Misfire mystery

You have gone through the ignition system from head to toe so I am going to say it is something else. I found that the jets in my carburetor were not drilled correctly so you may want to go through the carburetor and "blue print" it, meaning to make sure that everything is as designed. You can make a rig to flow test the jets for have them flow tested.

It is normal for a slight miss while not under load. The engine is really designed for running at its normal rpm and load and not at an idle or under no load. That is probably not the case here but something to keep in mind.

To manually set the ignition, search for the knee. With the car in neutral, use the hand throttle to set the engine at a fast idle. Start with the ignition lever in a slightly retarded position and increase the advance one notch at a time. The engine rpm should come up with each notch. If not, start with the ignition more retarded. At some position the engine rpm will not increase. That is the knee. Retard the ignition one notch and either remember that position or mark it. That is where you should be driving the car most of the time. You can retard the ignition one notch if under heavy load, especially at lower rpm. You can also advance the ignition one notch if you are cruising down the highway at a fairly fast clip but not much throttle. You can also search for the knee while driving the car on a level road while using the hand throttle.

Lower compression engines (stock) are more sensitive to ignition timing so if that is the case here, you may want to use more retard and advance under different driving conditions.
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Old 02-26-2024, 02:52 PM   #58
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Default Re: Misfire mystery

Removed the valves, too them to a friends machine shop for refacing.

2 are slightly bent, the rest are on the edge of usable.....

Im going to get a new set.
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Old 02-26-2024, 07:46 PM   #59
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New valves will help a lot. Buy a seat cutter or have someone cut the seats. Lightly lap the valves until there is a uniform grey ring where they seat. Make sure the guides are good. Quickly pull out the new valves with your finger on the bottom of the guides. There should be pop when the valves pull out of the guides.
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Old 02-26-2024, 08:24 PM   #60
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I have new guides
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Old 02-27-2024, 08:10 AM   #61
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Default Re: Misfire mystery

Sounds mechanical to me, not electrical. Particularly if you can here it at tailpipe. Perform a leakdown test on all four cylinders. It is a simple test similar to compression. That will test your springs, headgaskets, valves and valve seats, as well as rings. It can also help with diagnosing carbon deposits that can by itself cause detonation.

The erratic vacuum is the tip-off. Assuming gauge is correct.

Perform it cold and on a hot engine.

You will need compressed air and a quiet place if the gauge measures more than 25%. A leakdown tester can be rented from most good autoparts stores. You will need either a TDC whistle or a crank to move the engine. Remember to remove all four plugs during test.

Reply with the percentages for each cylinder to help narrow cause if it is a positive leakdown test.

Good luck,
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Old 02-27-2024, 10:39 AM   #62
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I have a leak down tester....

As of now, I have the top end off the engine, valves disassembled etc

Took the valves to a friends machine shop to have them refaced. 2 are slightly bent and the rest at the end of usability.

I ordered new valves, guides and springs. Seats appear to be ok
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Old 02-28-2024, 12:26 PM   #63
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Default Re: Misfire mystery

Fairlane514,
I wonder if the leakdown test would have been positive with the bent valves. It sounded mechanical to me, your backfiring. If the test were positive, it would have at least saved you some time.

Include pics of bent valves. That would be interesting.

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Old 02-28-2024, 03:06 PM   #64
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Default Re: Misfire mystery

Probably would have shown in leak down test.

The bent valves are hard to see, they were evident when my friend was refacing them. you could hear and see it while spinning. Only a little evident when looking at it in your hand.
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Old 03-01-2024, 05:55 AM   #65
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Default Re: Misfire mystery

Hi I had a bad back ire on my 30, it turned out to be the gasket on the carburetor was sucking air , you may check that as well if you had not found your problem.
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Old 03-01-2024, 07:37 PM   #66
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Ok, thank you

I believe I have found the issue.......valves not sealing.

I have new valves now, waiting to get the stems ground to proper lash.
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Old 03-03-2024, 12:21 PM   #67
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Default Re: Misfire mystery

I just fixed a friends car that had the back of the ignition switch bouncing off the gas tank (that’s scary even to think about LoL. That problem though is very very common if the original switch has been replaced.
This comment is only meant to reinforce your thoughts on that particular problem.
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Old 03-03-2024, 04:45 PM   #68
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Thanks, I checked that already, my switch Has flat screws, so they dont protrude into the tank. I also put some strips of electrical tape on the tank for insurance
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Old 03-29-2024, 06:44 PM   #69
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Im back...

Whats been done so far:

New valves, proper lash, and lapped in

New valve springs

New head and gasket

New coil

New ignition switch

New wiring (already done previously)

Fresh fuel

Tried two different carburetors

Tried two different distributors

New intake/exhaust gaskets

Ground strap to body and to transmission

Continuity from ground to distributor body

Still have an intermittent misfire....not consistent like a mechanical issue (valve or worn cam)

No backfires, revs up good, starts easy

Just seems like ignition related, its not cyclical, can be one misfire or several in a row. Spark plugs look the same on all four cylinders.
I can ground out the spark plug straps and hear a change on each cylinder.

GAV doesn't seem to have an effect. Vacuum gauge shows a dip at each misfire.

Valves appeared to open and close the same amount relative to each other.
(original lifters, non adjustable)

60 PSI compression on all cylinders

New Ammeter

I do have a flathead V8......I threatened my car with it.....didnt seem to help either.
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Old 03-29-2024, 07:30 PM   #70
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One thing I have not tried it bypassing the Ammeter.......
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Old 03-29-2024, 08:05 PM   #71
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Change the condenser. The present one might be randomly breaking down with change in temperature.
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Old 03-29-2024, 08:06 PM   #72
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I did that with a different distributor, no change
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Old 03-29-2024, 08:33 PM   #73
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You wrote that you installed new spark plugs. Are the metal gasket rings in place beneath the plugs? They seal the cylinders. If one is missing or a plug hasn't seated all the way against the cylinder head, you might be hearing and feeling escaping exploded gas. Also try adjusting the plugs to 0.032" to see if that helps.
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Old 03-29-2024, 08:35 PM   #74
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Seal rings are in place, they are gapped at .035 right now....Champions W18
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Old 03-30-2024, 09:35 AM   #75
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Wow you have the patients of a saint! I have little to add but be sure the distributor lock screw and jam nut are tight...you may want to be sure the screw is the correct one for Model A https://www.snydersantiqueauto.com/s...tributor+screw

I had a miss when driving with the lights on...I simply adjusted the third brush on the generator for more output and my miss disappeared. You could try a higher output charge.
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Old 03-30-2024, 09:48 AM   #76
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Default Re: Misfire mystery

I once had a similar problem. Turned out it was a worn camshaft.
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Old 03-30-2024, 09:54 AM   #77
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Fairlane,

I just reread this whole thread. Our coupe came with a newly rebuilt engine. Standing at the tailpipe, when the engine is warmed to operating temps, there are random puff, puff... .... puff, ... puff, puff, puff sounds. I too have chased all things mentioned. The car has plenty of power. A Nurex spark tester showed no misfires at the distributor cap. There are no documents of what components were put into the engine, but the former owner was told the engine has a touring cam.

I've been near only one other car that was making the same sound. The owner did not know what components were in his engine either. I described the sound to a professional Model A engine builder. After a few seconds of thought, he suggested that it might be the grind of a touring cam and its unique valve overlap and / or lift.

Our car performs well and has 18000 miles in the last 3 years on the overhaul. I've stopped worrying about it.
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Old 03-30-2024, 05:39 PM   #78
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I know its .020 over, it does the random puff puff sound at the tail pipe.

My vacuum gauge show a dip on the needle when it puffs.

I have the correct set screw/jam nut on the distributor.

A touring cam is an interesting theory....just a strange rhythm of puffs.

I dont feel a misfire when cruising, just idle. "Maybe" a little faint smoke when it puffs.....but not otherwise.
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Old 03-30-2024, 08:26 PM   #79
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I can make my A puff…….puff…puff………..puff, and I can stop it, it’s not puffing right now. I have a nice slow idle and mixture set halfway between to rich and to lean, idle is slow so the GAV has no effect at idle
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Old 03-30-2024, 09:01 PM   #80
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I assume you are suggesting a carburetor adjustment as the solution. I have adjusted this one, been through it more than once and tried another carb to no avail.

I have rebuilt many many carburetors, not all Zeniths, but I do know how to tune them.

I may order the Renner jet kit, but I measured all the jets and set them to spec.....now that doesnt mean they are flow tested, but the other carburetor had the same results.
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Old 03-31-2024, 09:44 AM   #81
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What happens if you increase the idle speed a little bit? And then a bit more?
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Old 03-31-2024, 09:50 AM   #82
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The higher the rpm, the less evident the misfire is. At cruising speed you dont notice it, or its no longer there
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Old 03-31-2024, 11:52 AM   #83
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Bypassed the ammeter, no change.

Have no resistance in the "power cable" to the condenser.

Top plate of distributor has good ground

6.40 volts at coil (engine off)
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Old 03-31-2024, 02:19 PM   #84
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Tried a new terminal box (old one was slightly suspicious) , no change

Rod Doe suggested a touring cam causing this......Havent been able to find much about the cam and the characteristics
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Old 03-31-2024, 02:54 PM   #85
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Any votes for a possible loose timing gear? would it be a random misfire? noisy?
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Old 03-31-2024, 03:48 PM   #86
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Trying to upload a video but its too large apparently....23 seconds long.

Im not good with computers...
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Old 03-31-2024, 06:26 PM   #87
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Pulled my spark plugs, pretty black at this point.

Checked my wiring from beginning to end for continuity issues etc.

I have 6.40 volts at the power cable to condenser. Engine off, key on.

Started to look at the carb again... I get response from the idle mixture screw, not so much from the GAV (seems like nothing)

I noticed on this particular Zenith 1, I have a jet in the bore of the GAV that can be removed for cleaning etc.
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Old 03-31-2024, 06:57 PM   #88
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A fellow posted on another place of his nice idling A after he timed it the Paul Shinn way and installing Renner’s flowed carburetor jets, it’s sweet to hear the exhaust note of a well tuned and running A tick tick tick tick
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Old 03-31-2024, 07:19 PM   #89
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Yeah, thats what Im trying to get......Im going to talk with Renners tomorrow.
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Old 04-04-2024, 08:16 PM   #90
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Received the Renners jet kit and rebuilt a third carburetor. No change in the misfire.

The carburetor is more sensitive to adjustment now with the Renner's jets.

Tried closing the spark plug gap to .030, thinking maybe a weak coil or ignition system having a hard time jumping the gap. No real change....

Its just so random, I cant say its a mechanical issues such as cam lobe etc.

My coil is an Oreilly Master Pro 6volt.

I did check my air gap at the distributor cap contacts and rotor. As the rotor first approaches I have just under .019, as the "blade" of the rotor passes to the end, I am over .025. Pretty consistent on all four.

Cap is new and I tested for carbon tracks or "bleed over" from one contact to another.
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Old 04-05-2024, 09:14 AM   #91
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"Checked my wiring from beginning to end for continuity issues etc."

Fairlane, I hear members of the local Model A club and occasionally others make the same comment. You might already know this, but just in case you or someone else doesn't:

Continuity is checked with an ohm meter. The ohm meter passes milliamps through the portion of a circuit bounded by the positions of the two test probes. Using an ohm meter, the circuit may test good when it is not capable of passing a legitimate load test. Milliamps are .000s (thousandths of one amp) In operation, the ignition on the Model A will draw ~ 4 amps, or ~ 4000 milliamps.

"Voltage drop" test methods are used to determine the quality of a circuit. You can find a series of voltage drop test procedures that will verify that your car's wiring is in good shape, marginal, or poor condition in Les Andrew's blue book, "Troubleshooting and Diagnosis", Chapter II.
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Old 04-05-2024, 11:09 AM   #92
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Rob, I agree with what you are saying, and that is something I have not done.

I was giving the benefit of the doubt to the new wiring, etc.

As random as it is, it seems a weak spark or ignition system may be more plausible.

Im going to focus more on that.

Thanks
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Old 04-05-2024, 11:27 PM   #93
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A thought - my coupe will run out fine and idle very smoothly when first started and a short drive. When warm the engine will sound like a slight misfire but no knock or backfire etc. The suspect in my case is carbon in the cylinder head - with clean plugs. Engine does not smoke and pulls strong. It was rebuilt in 1979. As noted it only does this when warmed up.
Just a thought- you have many qualified suggestions and good support. All the best with your search .
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Old 04-06-2024, 07:42 AM   #94
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Quote:
Originally Posted by Fairlane514 View Post
Trying to upload a video but its too large apparently....23 seconds long.

Im not good with computers...
I’am out of ideas, a shorter video ? sure might help
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Old 04-06-2024, 08:02 AM   #95
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I had the head off and cleaned the pistons etc of carbon.

My friend has an oscilloscope which Im going to attempt to use.

I also was going to try an epoxy filled coil in place of the oil filled one I have installed now.
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Old 04-07-2024, 07:33 PM   #96
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Here's today's find......

The only component of the ignition system I had not replaced was the small armored cable from the ignition switch to the condenser.

I had 6.4 volts at the ignition switch and to the brass contact at the end of the wire. So I wanted to attempt a voltage drop test. Results were nothing definitive.

As a last resort, I performed a Mr. Spock mind meld and asked the car what was wrong. No immediate answer....

I kept staring at the armored cable (mine is the small aftermarket one).....I started to wiggle it around and the next thing I know I got a smoke signal from deep in the tunnel under the dash ( I had the dash out ). Turned off the key and disconnected the battery.

So.....my theory, it was able to carry voltage with key on engine off, but had voltage drop while running, causing a weak spark.
Pulled the cable wire out and found a black burned looking area about and inch and a quarter long. There are places in the "conduit" that feel crispy or stiff.

I will attempt to download some pictures.
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Old 04-07-2024, 07:43 PM   #97
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https://www.fordbarn.com/forum/attac...1&d=1712536977
Attached Images
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Old 04-07-2024, 07:45 PM   #98
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First picture is the armor unwrapped to show the black cloth then white plastic insulation

Second picture is the "burned area" I found after removing the cable

Third is the armor unwrapped at the burn site.
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Old 04-07-2024, 07:57 PM   #99
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Persistence pays off.
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Old 04-08-2024, 06:55 AM   #100
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X2 on congrats. Your post describes a failed ignition cable. I also like your theory. The post implies that the misfire condition, which you have been looking for, is now gone.

I'm hoping this is true????
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Old 04-08-2024, 07:03 AM   #101
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There are ways to use jumper wires to temporarily bypass virtually all of the normal ignition circuit wires. The vendors sell a jumper for bypassing the large cable from the coil + to and through the ignition switch and down to the distributor. I have two of them in my 'on board' tool bag. One I made and another purchased.

If you are running the modern style upper plate, mine is from Nu Rex, a jumper is easy to set up with a plain 16 gauge wire and a small tie wrap. I believe Nu Rex sells a set that allows for a quick plug and play example for roadside repairs.
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Old 04-08-2024, 09:07 AM   #102
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You are correct, what I have seen on vendors sites is a roadside cable. It has the screw in end and then on the other end an alligator clip to clip to the positive side of the coil (positive ground system).

I could probably make one from the remainder of my cable and see if this really is the fix.

https://www.snydersantiqueauto.com/p...6239&cat=41721
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Old 04-08-2024, 12:41 PM   #103
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The Nu Rex one is different and does not require removing the distributor. Your light weight cable probably unscrewed from the distributor without removing the distributor from the engine. If the car had the stock switch and heavy cable with the hold down clamp on stud #8, the distributor has to unscrew from the cable rather than the cable from distributor. It's best to drain the coolant down below the head to prevent a head gasket failure.

I had to search the Nu Rex site to find theirs.
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Old 04-08-2024, 04:36 PM   #104
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I have the NuRex ignition switch that looks like the pop out. I also have the small cable that unscrews from the distributor without removing it.
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Old 04-09-2024, 06:21 PM   #105
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So tell us please your remedy for the situation. It’s been an interesting thread and I hope you can now offer a solid result re. parts and adjustments. Thanks for your persistence and patience and from the many Barners offering input . Did you end up with a heavier cable?
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Old 04-09-2024, 06:54 PM   #106
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Today's shenanigans ........

While waiting on the new cable, I decided to try and salvage the old one. I cut off the affected area (what I could see) and spliced new 14 gauge wire in place.

No change, same misfire and puff puff in a random sequence.

I dropped the exhaust (new Aries) and started it, no change, just louder...

It could be the remaining original ignition cable is still bad.

I ordered the same small cable, but apparently they are out of stock with no ETA, so they are sending the heaving cable......the wire inside is probably the same gauge as the small cable....
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Old 04-09-2024, 09:21 PM   #107
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Quote:
Originally Posted by Fairlane514 View Post
Today's shenanigans ........

While waiting on the new cable, I decided to try and salvage the old one. I cut off the affected area (what I could see) and spliced new 14 gauge wire in place.

No change, same misfire and puff puff in a random sequence.

I dropped the exhaust (new Aries) and started it, no change, just louder...

It could be the remaining original ignition cable is still bad.

I ordered the same small cable, but apparently they are out of stock with no ETA, so they are sending the heaving cable......the wire inside is probably the same gauge as the small cable....
Many thanks and an interesting discussion. The mention of the puff puff sound
( mentioned by others ) also rings a bell at times for me and our Coupe.
Good luck with the new cable and we will see you on the FORD road….
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Old 04-09-2024, 11:03 PM   #108
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https://www.youtube.com/shorts/RxZxK0TB8SY


This is not my car, but mine sounds similar to this..

You have to turn it up to hear the puffing
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Old 04-09-2024, 11:10 PM   #109
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I have a similar problem at idle and runs great otherwise with lots of power. Most of the guys in our circle of Model A's brush it off and say "It's a Model A - what do you expect?" For a long time I still pressed on looking for the magic silver bullet. Still haven't found it. Something within the 95 year-old engine which has been fiddled with and had umpteen sets of valves, valve seats and so forth - is off and I just can't find it. I have come to the conclusion that dealing with what I have is cheaper than going for a whole new engine. It just doesn't run as smooth as my 2022 Honda.
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Old 04-09-2024, 11:48 PM   #110
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https://www.youtube.com/shorts/XKCX0bjRjEw


This is my car.....
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Old 04-10-2024, 01:49 AM   #111
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One thing I notice ,is every time there is a little click click in the engine ,the vacuum drops.
Maybe in the valve train, sticky valve,?
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Old 04-10-2024, 05:28 AM   #112
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Our coupe's puffing is much more noticeable. Is your car's puffing at the tail pipe more pronounced in person than on the video?

Is your vacuum gauge dampened?

The idle seems a bit fast. I haven't done it for a couple years, but if I reset the base idle and iteratively work it down to a slow idle with timing fully retarded to ... say 4 degrees ATDC, the puffing is gone. I run at 500+ rpm to keep blinking out of the LED headlights. We drive at night some.

I check my timing with a test light after locking down the distributor cam to see how many notches of spark advance turn the test light on. I'm usually set at the second notch down from the top.
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Old 04-10-2024, 05:59 AM   #113
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Thank you for the video !
For me your idle speed is high, your timing is advanced by either the hand level or base timing .
With a fast idle the carburetor is starting to pull fuel through the GAV, at a slow idle your GAV should not have any effect
At one puff I saw a whisk of black smoke, black smoke = unburnt fuel
I would move the hand lever up, slow the idle down and adjust the idle air. If you insist or need a faster idle , pull the timing lever down and pull the hand throttle down. I believe Ford talk of a rolling slow idle
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Old 04-10-2024, 08:42 AM   #114
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All new valves and springs

Yes, Idle is a little high, I need to get another video, but it does the same thing at slower idle. The puff is more pronounced in person than on the video.

My timing is controlled by the Nurex automatic timing system, so my spark lever is not really involved unless I want to go way too far advanced. My timing is set with lever all the way retarded.

It had the same misfire with the original spark advance by lever system. I put the automatic advance in when I changed the valves, head and gasket.

Yes, there is some black smoke when it puffs, indicating rich. I have the Renners jet kit in this carburetor. Plugs are sooty when I remove them. When I lean out the carb the worse it runs. My GAV had no effect at this idle speed.

I will try to get another video at a slower idle.....Its just easier to see the dip in the vacuum gauge at this idle, slower idle, the needle seems more erratic.

My gauge is not liquid filled
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Old 04-10-2024, 08:48 AM   #115
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My thought was with the damaged ignition cable, I had a weak spark and the unburnt fuel was the result.

I still believe its an ignition issue, but sometimes it helps with other opinions, as I get too focused on one thing.

I do wonder about camshaft and components, but it seems like that would more be more rhythmic.

The puff of black smoke........weak spark......too much fuel...

I will try to get a better video later today

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Old 04-10-2024, 09:31 AM   #116
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You can pinch the hose on the gauge between two fingers and a thumb, as I remember. Like pinching a garden hose and then release the pinch a bit to smooth out the gauge. I've read that a 4 cylinder engine's firing a cylinder every 180* is too far apart for an undampened gauge??? It works on mine.

You can set your base idle with the manifold gauge also. There is also a WWII youtube video that describes how to use the gauge to id many issues.
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Old 04-10-2024, 11:48 AM   #117
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Mine sounds exactly the same. Worried about it for a bit and, like you, couldn't find anything. Finally ran across and article that said it's "the nature of the beast". Stopped worrying and moved on.
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Old 04-10-2024, 04:06 PM   #118
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Fairlane, I fixed a similar problem on a friend's Buick. It had amiss that moved to every cylinder. I could run it at a slow enough rpm that you could see no spark alternating from one cylinder to another. That ruled out lots of the things. I took the distributor and an ohm meter and kept testing the wire going to the points. One time it would have current next time not. Turns out the wire going through the bakelite insulator in the side had gotten wet at some time in 100 years and had a rust spot RIGHT where the wire had hardened and cracked the insulation. It grounded whenever it wanted to causing the miss. I was lucky to find it. Replaced the wire and insulator and problem was fixed. Not saying this is your problem but the little things matter and can drive you nuts. This car had that miss for 20 years.
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Old 04-10-2024, 06:44 PM   #119
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Thanks everyone for the responses....

I have tried two different distributors, one has the new style points/condenser, the other has the original style...no change

Could be the nature of the beast, I hate to admit defeat.....

Im going to try cleaning my plugs with a propane torch. I would be inclined to leave it alone, but it if causes my plugs to soot up regularly......hard to ignore.

Could get any video today, but plan on working on it tomorrow ....
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Old 04-10-2024, 08:18 PM   #120
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In the early part of the video in post 110 it looks like the #1 spark plug is firing between the base of the porcelain insulator and the steel spark plug base. I.E. the plug is shorted to ground. You can see the spark jumping.
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Old 04-10-2024, 08:51 PM   #121
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Thanks for spotting that....

I ran the engine tonight in the dark and did not see any sparks or fireworks at the plugs etc.

Anyone think the timing gear could be a tooth off and still run ok?
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Old 04-10-2024, 09:16 PM   #122
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In the early part of the video in post 110 it looks like the #1 spark plug is firing between the base of the porcelain insulator and the steel spark plug base. I.E. the plug is shorted to ground. You can see the spark jumping.
I agree that there is a stray spark arcing in area of #1 plug.

Look closer while running in dark garage to track down stray spark.

I sometimes see the brass spark plug "wire" where it connects to distributor terminal, juggling around at same time as that flash near #1.


Also there are drops of water coming out tail pipe. This tells me that engine is NOT warmed up.

I will bet that plugs are fouling ... this will cause the missing.

I saw this MANY times with cars in 50s and 60. Too much idling and short trips where engine never warms up will foul plugs every time

You can clear up fouled plugs by running the car for 15 or 20 minutes at speeds of 35 or 40. A 10 mile run at 45 is even better.

Old time Mechanics in 50s called it "blowing out the carbon".

When checking plugs remember to look at the Porcelain part of plug.

Ignore the "steel ring" on plug it will be black because that area never gets as hot as the Porcelain.

Porcelain should be gray or brown or tan color.

It is normal for steel "ring " on bottom plug to be black.

I would not expect any OLD TIME engine that is idled for long periods and never warmed up to idle correctly.

This never happens with newer cars because computers control mixture.

My 1969 and 1973 Electronic Fuel Injected VW Fastback did not foul plugs.

This car has a computer that controls fuel injectors.

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Old 04-10-2024, 09:49 PM   #123
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Thanks Benson

I did check the engine running at night and saw no sparks escaping.

My dad has a 31 Roadster, starts up cold and goes into a very nice idle, no misfire etc. Now, his is 12 volt negative ground with a FS Ignition distributor.

I have a different distributor cap on it now, like a modern style with regular spark plug wires.
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Old 04-10-2024, 10:04 PM   #124
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Quote:
Originally Posted by Fairlane514 View Post
Thanks everyone for the responses....

I have tried two different distributors, one has the new style points/condenser, the other has the original style...no change

Could be the nature of the beast, I hate to admit defeat.....

Im going to try cleaning my plugs with a propane torch. I would be inclined to leave it alone, but it if causes my plugs to soot up regularly......hard to ignore.

Could get any video today, but plan on working on it tomorrow ....
My plugs do not soot up. They all run evenly clean even with the "puff".
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Old 04-11-2024, 07:26 AM   #125
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My neighbor's antique had a slight water leak at the top hose. The water trickled down the hose and around the first spark plug. It flash rusted under the plug gasket and caused a sometimes miss because the plug was not grounded properly. He would put in a different plug and get rid of the miss and think he fixed it because it now was grounded. One time I removed the plug and cleaned the film of rust and put the same plug back in to prove to him what was happening. He never did fix the water leak. Something small is hiding from you. You are looking to hard.
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Old 04-11-2024, 08:06 AM   #126
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I get what you are saying..

BTW no water leak there
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Old 04-11-2024, 08:24 AM   #127
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In the wee hours, I keyed in something akin to the following text. Apparently, I never hit the 'post' button...

I used the magnifier to watch the video. I set it at 350 percent and watched many times while the video wrapped.

The first thing I noticed was that there is smoke coming out the tail pipe at a steady flow. There is some debris in it. Maybe its water as stated above.

The next thing I did was practice double clicking very fast to stop the video and advance only a few frames at a time. When the camera returns to the engine, I have moved the view to the lower right corner of the images. It took a while to achieve this. What shows up is a flash that appears to be a front exhaust port leak. This is followed by flashes that light up the front right corners of the engine and the flat edges near the timing gear cover?? There are multiple flashes that light the right front edge of the engine head.

After multiple attempts, I was able to freeze on a frame that shows the flash at the plug along with a large white flash reflecting off the right front corner of the head. I have not come up with a great explanation for this. Perhaps an early owner of the car is messing with Fairlane and us!

I would like to see a new film shot from a better view of the right front corner of the engine.
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Old 04-11-2024, 09:34 AM   #128
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Hey Rob, thanks for the all the hard work...

I will get more video today.

If you can think of any other angles, let me know.

I do have a different distributor cap on it now, the more modern style with plug wires.

Yes, it does seem a little smoky, and I notice it as well. The condensation is the other thing....its Texas

Would the flash be possible from the two blade cooling fan reflecting light from the sun?

I also ran it last night in the dark.....I did not see any flashing or sparks.....
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Old 04-11-2024, 10:01 AM   #129
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"Anyone think the timing gear could be a tooth off and still run ok?"

A Model A engine will run with the timing gears one tooth to the left or right of the index marks. But all is not well if that's the case. I have repaired at least three sluggish engines in the past three years in older restorations, whose fiber timing gears were ostensibly lined up properly with the steel crankshaft gear - but the crankshaft index mark had been stamped in the wrong place by one tooth! There were a ton of these inferior gears imported in the 1970's and sold almost exclusively through an unnamed Model A parts vendor in Kansas, who knowingly bought defective parts at a major discount from the national distributor who had rejected them - and then sold them at a lower price than honest vendors could. Knowing the "parsimonious" nature of many Model A owners, guess who they ordered the parts from! There are probably lots of those gears still running in Model A's, whose owners don't know what a Model A engine should run like. With mis-aligned timing gears, the engine WILL run, but it will be sluggish in performance. The index mark on the steel crankshaft gear should be located one tooth to the right of the keyway. The defective gears were marked opposite the keyway, effectively beginning the engine's life in a retarded condition that can't be overcome by advancing the distributor's cam when setting the initial ignition timing. The only fix is to move the camshaft gear one tooth counterclockwise and ignore the index mark on the steel gear. Not a lot of fun to do this, but that's the only way to overcome a defective crankshaft gear's index mark.
If Fairlane 514's engine performed satisfactorily before this misfire problem reared its ugly head, I wouldn't think mismatched timing gears are to blame.
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Old 04-11-2024, 10:13 AM   #130
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I also used my thermal gun on the cylinders and exhaust manifold etc.
All appeared to be pretty even in temperature.

Used my screwdriver stethoscope and couldn't really hear anything unusual.

Marshall.....the misfire has been there since I bought the car in December.

Nothing has improved with the parts I have changed or adjusted.

Something I have not checked is the timing gear. That was my next attempt to discover the problem.
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Old 04-11-2024, 03:57 PM   #131
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https://www.youtube.com/watch?v=0yMT04PlDo8

Second video

I did remove the side inspection cover, and I have an aluminum timing gear, with all teeth intact and crisp, no wear etc

Removed the timing cover and the alignment "dots" are in the correct position one tooth to the right of the keyway.

Last edited by Fairlane514; 04-11-2024 at 07:30 PM.
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Old 04-12-2024, 10:12 AM   #132
Rob Doe
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Default Re: Misfire mystery

Fairlane, I don't hear the same puff, puffing that our coupe has in your second video. You are likely correct about the fan blade, but to be certain, perhaps holding a piece of cardboard between the fan and the engine with the same setups would verify the theory.

The unevenness of the flashes might be explained by a wandering of the fast idle by several rpms.

Pinch the black hose between your first two fingers and release slightly. Control this release amount with your thumb. The gauge may smooth out a bit.
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Old 04-12-2024, 12:49 PM   #133
dansluck
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Default Re: Misfire mystery

Good Job on a Tough Find
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Old 04-12-2024, 01:15 PM   #134
Fairlane514
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Default Re: Misfire mystery

I have pinched the hose, just not on video. Did not do much...

Im certain the fan and sun reflection are causing the flashing. I tried blocking as much sun as I could, but some still got through.

Verifying my cam gear is correct and installed properly eliminates mechanical timing being the issue, unless major lobe wear......cant really look at that without removing the cam and measuring. Maybe lifters as well.

When I had the head off and replaced the valves, springs and guides, I did roll the engine over and verify everything functioned as it should. I did not measure the valve lift from the seat. My lash is .013 Intake .015 exhaust

So, I'm back to ignition timing. Im suppose to get my new armor ignition cable today, so maybe I will know something in a couple days.
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Old 04-12-2024, 07:20 PM   #135
Fairlane514
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Default Re: Misfire mystery

I think im going back to the fundamentals of the ignition system.

Quadruple check everything again...

May even consider a Pertronix Ignitor I.......Yes, I said it.....
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Old 04-13-2024, 06:56 AM   #136
noboD
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Default Re: Misfire mystery

Step back away from the ledge. Things are not that bad. You would just introduce another problem by doing that.
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