Engine stumbles on acceleration

[Neshkoro]

Hi folks,
I need some help.
I bought this 1930 Model A Ford Tudor last September. I've been going through some things that need attention. I just finished rebuilding the steering box, did a tune up. New plugs, cap, rotor, ignition coil and condenser. The points looked good. I just finished rebuilding the Tillitson Carb. The car starts and idles good. While driving, if I accelerate, it begins to stumble and bog down. I've checked the timing and the points gap and they seem to be correct. Fuel flow to the carb is good. I checked the compression. They range between 50 and 60 PSI. I've installed a fuel filter between the gas tank and the carb.
THOUGHTS?

Thanks,
Bill

[Jacksonlll]

Take the filter off and try it.

[700rpm]

I agree with JacksonIII. FIlters are unnecessary unless you’ve got rust dust in your gas tank, and that is best resolved with a pencil filter at the shutoff. Otherwise your sediment bowl should be adequate. If you have the steel bulb type sediment bowl, open it up and make sure it isn’t clogged.

[Slowmotoring]

Is your gav set properly? Might be running it lean

[Marshall V. Daut]

Check your "Private Messages" in the top right corner of this webpage.
Marshall

[Neshkoro]

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Marshall,
Thanks for the PM. I'll remove the fuel filter and do as you suggested. I wont be able to get back to the for a couple of weeks. As soon as I do, I'll reply with the results. Thanks so much.
Bill

[Marshall V. Daut]

Only any fuel filter between the sediment bowl and carb, not the pencil filter inside the gas tank or the round filter screen inside the sediment bowl. See that the sediment bowl screen is clean. Also remove any external air filter on the back of the carb to test if that's affecting the acceleration by choking fresh air intake.
M.

[Ayers1]

I had something similar happen with mine. Turned out the aftermarket shaft between the distributor and oil pump wasn't locking in properly. Idled great but ran like crap when you revved it.

[whirnot]

On a side note, you said the points looked good and you adjusted them. I would recommend as a matter of habit, when doing a tuneup, always replace the points. They are inexpensive and without dressing them you will not get a proper gap setting due to the burning away of material.

[700rpm]

Originally Posted by Marshall V. Daut

Only any fuel filter between the sediment bowl and carb, not the pencil filter inside the gas tank or the round filter screen inside the sediment bowl. See that the sediment bowl screen is clean. Also remove any external air filter on the back of the carb to test if that's affecting the acceleration by choking fresh air intake.
M.

I have high respect for Mr. Daut, but my experience re: pencil filters vs inline filters is just opposite of his. I ageee on the sediment bowl advice.

[GRutter]

Originally Posted by Neshkoro

Hi folks,
I need some help.
Thanks,
Bill

Hi Bill -
Please edit your profile and add your location. You may have other members close by that could help you out.

[ArtimusGordon]

Just a thought...try loosening or removing the GAS CAP? Also you could check the gas FLOW at the carburetor. Try changing to a known working carburetor.

[Patrick L.]

It sounds as though you may be running a bit lean. Open the gas cap and open the GAV [ choke rod] to 1- 1.5 turns and also the idle mix screw.

I'm one of the few that uses an in-line fuel filter with no issues.

[Herb Concord Ca]

When I bought my P/U 30 years ago it had an in-line fuel filter and continues to have one today. Never had a filter problem.

[Neshkoro]

Patrick L,
You mentioned the idle mix screw. Turning the screw in or out makes no difference at all on how the car idles. Although, once it warms up, it does seem to idle OK. I placed an order for a bunch of ignition parts. As soon as I can, I will try the things that you folks suggested and report back.
thanks again.

[Patrick L.]

You might have the idle speed a bit too high if the idle screw does nothing. Or the idle passages didn't get cleaned enough. The idle mix screw adjusts air not fuel.
These carburetors are pretty simple and it usually takes a lot of cleaner and compressed air to get them clean. A tag wire worked thru the passages is usually needed, then flushed and blown clean.

[Sparky]

It may be a long shot, but last year my car started running rough when accelerating and also had higher than normal fuel consumption. The cause was the compensator jet in the carb had come loose resulting in a rich mixture. A quick snug-up with a screwdriver and all was well.

[Neshkoro]

I’m going to check the idle speed once it warms up and will set it as low as I can get it to idle. Then I’ll try to adjust the idle screw. The bottom half of the Tillitson carb is warped. It will seal on the air inlet portion or the fuel bowl portion. I chose to get it to seal better on the air inlet portion. The top portion is easy to flatten out with a piece of sandpaper and a flat plate. The bottom half, not so easy!

[Patrick L.]

The Tilly's are prone to warpage.
I've been able to straighten them out by sanding and filing.
Some folks have a way to do it in an oven/stove.
When you try to remove the main jet you have to be careful not to ruin the threads.

[Sparky]

Oh, I missed that detail about the Tilly carb. My suggestion doesn't apply, I think.

[mass A man]

You may want to consider a rebuilt "Marvel-Schebler" carburetor made to replace the Zenith's for the Model A's.

[Oldgearz]

Recently rebuilt me B carb for my 30 Coupe and the car stumbled badly on acceleration. Took it apart and compared new parts to old parts and found the main jet on the new part was considerable narrower in diameter than the old part. Put the old jet back in and the car runs perfect. As is nearly universally agreed, some reproduction parts just don't muster up. Compare the parts you took out to the new parts you put in.

[Neshkoro]

Good idea on checking parts. I did rebuild the carb before I did any serious driving. I’m going to check that, too!

[Neshkoro]

Here's an update on the stumbling problem.
I disassembled the carb and checked the various jets and their diameters compared to the old ones and some specs form the Model A Ford Carburetors book. All were tight and the correct diameter. Earlier I disassembled the carb and drilled out the plugs to clean the hidden ports. Plugged the holes by tapping and installing set screws. The new welch plug was epoxied in place.
Now, there is a new spark plugs, new coil, new condenser, new coli wire, new rotor, new style cap and plug wires.
I ordered a new set of points from Ecklers. When I went to install them, first they would not fit on the pivot pin in the distributor. Then the other contact would not screw into the contact block. I will be calling them Monday.
The old contact fit nicely in the new block so I polished the contact surface of the old one and re installed it. Same for the points. I polished the contact and reinstalled them. I'm going to call Ecklers and ask for another set or a refund and then reinstall them.
So, after all that I reset the points gap and the timing and went for a ride. One thing I did notice was if I really adavanced the timing on the steering wheel lever, it did run a bit better. Much less stumbling and backfiring than before. I've been using one of those Nu Rex cam wrenches to set the cam. I think I must have the timing off somewhat. That is such a pain to get to TDC with the timing pin. I never feel that I'm perfectly sure I'm at TDC.
Anyone like to chime in with their thoughts?
Thanks again.
Bill

[GeneBob]

You have not stated where you normally fun the spark advance lever. Generally, once the car fires up, you want to be like 2/3 to 3/4 of the way to full advance on the lever. Do not over think the spark advance, start it, then advance it and leave it there unless you are idling for an extended period. BTW, not to be insulting, are you sure the advance lever was all the way up when you set the timing? The NuRex wrench instructions say to turn the cam two revolutions (CW) before setting and locking the cam. (You want all the play in the distributor to be taken out when you reach the set point.) If you miss the point where you are supposed to lock the screw, do not back up, go around another turn or you will not be timed correctly. The tricky part is that the cam screw wants to tighten as you are turning the cam wrench. Hope you find the problem and enjoy driving!
As far as your timing pin being at the bottom of the timing mark, I always felt the same way but, in reality, you won't be off by more than maybe 3 degrees. You can fine tune after you solve the major issue.

[abachman3]

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Are you advancing the timing, left lever on steering column about 1/3 - 1/2 of its travel distance when driving? You need to advance the timing in order to get it to run properly. Also, as mentioned above, the GAV, (choke rod) needs to be opened some... each carb will be different, but a good starting point, after warmup is about 1/4 - 1/2 turn open.

[GRutter]

Originally Posted by Neshkoro

I ordered a new set of points from Ecklers. When I went to install them, first they would not fit on the pivot pin in the distributor. Then the other contact would not screw into the contact block. I will be calling them Monday.

There have been many threads regarding inferior parts quality and issues being billed or receiving refunds from MACS / Ecklers.

Just a suggestion, but you might want to use vendors that support these forums such as Berts, Snyders, Brattons and others, that specialize on Model A Fords, are knowledgeable, will answer your questions etc.

Look at the "sticky" post at the top of the Model A Forum, and look for Parts Houses, or for the particular product or service you need. You'll benefit from the collective experience of many users recommendations, as well as dealing with vendors offering quality parts

[Neshkoro]

Good advice. Thanks for the heads up.

[Ed in Maine]

Some may disagree with me but get rid of the Tillotson Carb and get an original Zenith. Clean it and check that all flow passages are clear. Flow test the jets so you know how much gas you are putting into the engine. Reassemble with a new gasket set. Maybe you should add a new float valve with a soft seat. You can't miss! Ed

[nkaminar]

Neshkoro,

Welcome to the forum.

Unless there is something wrong, the fuel mixture ratio and timing can be manually adjusted on a Model A for the best engine performance. Do this when accelerating or running up a hill with the throttle open. The timing should be advanced until further advance will not provide any better performance. This is the "knee" in the timing. You can test the knee by slightly retarding the ignition until the performance starts to fall off and then slightly advance it. The GAV knob can be adjusted for the best performance in much the same way. Enrichen the fuel mixture by turning it counter clockwise until the performance starts to fall off then turn it clockwise until the performance starts to fall off. Somewhere in the middle will be the best performance. If these adjustments do not work to cure your poor performance, then there is something wrong. Look for a vacuum leak in the carburetor, either at the flange, the throttle shaft, or elsewhere. Or a fuel flow issue. Try a different carburetor.

[GeneBob]

Check for a leak in your intake manifold or intake gasket. You can spray WD 40 or starter fluid around the base of the manifold and carb mount area to check for leaks.
Is the generator charging? Does it stall when you turn on the headlights?

[Apperloo]

Side note: I luv the colour of your ccpu

[Neshkoro]

I will check for manifold leaks. It does not stall when turning on the headlights.
It will be a while before i can check things.
I'll let you guys know what I find.

[neds29]

My advice: lose the Tillotson. I finally took mine off after 4 years of messing with it (leaked from warpage which was dangerous and not fixable) and replaced it with a Zenith. Very happy now.

[Neshkoro]

I've more or less exhausted all other ideas. That might have to be my last resort.

[Neshkoro]

I forgot to mention a couple of things. Some time just after I bought the car I bought a new modern style distributor cap and resistor plug wires. Do you guys think those changes have any thing to do with the stumbling?

[daren007]

I happen to like my Tillotson.

[jquinlan]

Originally Posted by Neshkoro

I think I must have the timing off somewhat. That is such a pain to get to TDC with the timing pin. I never feel that I'm perfectly sure I'm at TDC.
Bill

Bill, one of my favorite Model 'A' tools is the spring loaded gizmo that helps you find TDC. Most of the parts suppliers sell these and they make tune up's a lot easier for me. https://www.brattons.com/timing-calibration-tool.html

[Neshkoro]

I saw the spring loaded pin advertised. Maybe I'll buy one. What's another $20.00!

[GeneBob]

If you switched to a modern distributor cap, how are you using the NuRex wrench to set your timing?

[Neshkoro]

I installed the original cap, set the timing with the Nu Rex wrench and then swapped the old cap for the modern cap. Do you see anything wrong with doing it that way?

[GeneBob]

It sounds logical but I dont' know if the spark plug locations in the modern cap are in the same locations. If the modern cap has different clocking relative to the tab that engages the distributor body, your timing will be different. Can you check it with a timing light? I forget if you said that you had done that.

[Neshkoro]

I haven’t checked the timing with a timing light. I’ll do that and check back here.

[arnhemmer]

If you a vacuum wiper motor check it and the hose for possible leaks.

[aermotor]

Originally Posted by arnhemmer

If you a vacuum wiper motor check it and the hose for possible leaks.

Get it started and running at the lowest idle speed and spray carb. cleaner around the manifold to block areas and if you get an increase in RPM chances are a intake gasket leak. Quick acceleration, not only from idle, has to start with a rich mixture and intake leaks will cause a lean mixture.

John

[Neshkoro]

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The vacuum wiper port on the manifold is plugged, temporarily, while I rebuild the wiper motor. I did change the manifold gaskets some time back. I will try spraying the carb cleaner on the manifold.
Thanks for the ideas.

[GeneBob]

I had another idea on the timing if you are having trouble setting up a timing light. I know it is a pain the first time because there is no mark on the pulley or pointer to go by.
Set the timing using the NuRex wrench and the original style cap, then keep the original style cap in place when you run it and see if that fixes the hesitation. Then you know it is a difference in the two distributor caps.

[Neshkoro]

Another good idea. Thanks. I'll try that!

[Rob Doe]

Nice thread. Timing is right for me. Thx.

[Neshkoro]

Yesterday I changed the plug wires from resistor to solid core. It made a significant difference in the way it ran. Cleared the stumbling 90%. I compared the old distributor cap with the new modern cap. They are virtually identical. I checked for air leaks around the intake manifold. That’s all good. I used the unlit propane torch method. I did put an extension on the carb intake to make sure I wasn’t sucking any propane into the carb. Today I’m going to remove the fuel filter and check the timing with a timing light. I did a vacuum gauge check and the gauge reads between 18-21 inches of vacuum. A little bouncy! I still can’t get it to idle low enough. That causes gear shifting problems. A low enough idle causes it to want to die when coming to a stop. More testing to come. I may have to take the plunge and buy a new carb.

[Neshkoro]

I changed the fuel line to remove the filter. No change in the way it runs. I made a timing pointer (photo attached) to check the timing. Timing was right on. Looks like it's time to buy a another carb!

[BigGameJames]

Hello all,

New member here.

Looking forward to learning a lot from you all.

[Neshkoro]

So, i completed all the things discussed in the above posts except the carb replacement.
The car runs 90% better than it did before. No more backfiring. The two things that made the biggest difference were verifying the timing was correct and changing from reistor plug wires to solid core wires.
The addition of the timing pointer was a big help. I cut a small notch in the crank pulley with my Dremel grinder and put some silver paint on it.
See attached photo

[Y-Blockhead]

Originally Posted by Neshkoro

Marshall,
Thanks for the PM. I'll remove the fuel filter and do as you suggested. I wont be able to get back to the for a couple of weeks. As soon as I do, I'll reply with the results. Thanks so much.
Bill

Originally Posted by Marshall V. Daut

Only any fuel filter between the sediment bowl and carb, not the pencil filter inside the gas tank or the round filter screen inside the sediment bowl. See that the sediment bowl screen is clean. Also remove any external air filter on the back of the carb to test if that's affecting the acceleration by choking fresh air intake.
M.

Originally Posted by 700rpm

I have high respect for Mr. Daut, but my experience re: pencil filters vs inline filters is just opposite of his. I ageee on the sediment bowl advice.

So let me get this straight. Marshall recommends to remove "only any fuel filter between the sediment bowl and carb" but leave the pencil filter in (to which I agree) but you are saying the opposite, to remove the pencil filter and put an aftermarket filter between the sediment bowl and carb?

[katy]

Originally Posted by Neshkoro

New plugsl

What spark plugs did you use? What did you gap them at?

[Neshkoro]

.035 and Champion plugs, if I remember.

[oldredford]

My sometimes does stumble on accel. I adjust the GAV to let more gas in. Cures the stumble.

[Neshkoro]

I tried that. It didn't seem to help much. The A runs pretty good now. As good as you would expect a 90 year old car to run!!!
Thank you all for all your help.
Motor on!

[Bill OH]

Set your plugs to .025 on a 6v system - try that. .035 is pretty wide.

[Neshkoro]

I’ll try that.

[redmodelt]

Originally Posted by aermotor

Get it started and running at the lowest idle speed and spray carb. cleaner around the manifold to block areas and if you get an increase in RPM chances are a intake gasket leak. Quick acceleration, not only from idle, has to start with a rich mixture and intake leaks will cause a lean mixture.

John

I have found when using carb cleaner to check, if there are vacuum leaks, the motor wants to cut out not increase in RPM.

[Neshkoro]

That's an interesting thought! The good thing about carb cleaner is that it evaporates. Doesn't make a mess as WD 40 would! I tried the propane torch method but I got no difference. (Torch not lit!)

[Neshkoro]

Bill OH,
I tried regapping the plugs. I thought.025 was a bit tight so I went down to .030”.
I went for a long ride to check it out. To me, it ran OK but I think it ran better at .035”
I filled up the gas tank and added some Marvel Mystery Oil.
Somebody asked the type of plugs I’m using. They are Autolite.

[katy]

Originally Posted by Neshkoro

Bill OH,
I tried regapping the plugs. I thought.025 was a bit tight so I went down to .030”.
I went for a long ride to check it out. To me, it ran OK but I think it ran better at .035”
I filled up the gas tank and added some Marvel Mystery Oil.
Somebody asked the type of plugs I’m using. They are Autolite.

.035" is the Ford recommended gap.

Saying that the plugs are Autolite is like saying the car is a Ford or whatever.
What number are the plugs?

[Neshkoro]

Autolite ASP 3076 Sorry. I forgot to add the part number.
They are from NAPA and the only number they offer.

[GeneBob]

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Question for diagnostic purposes. Does it stumble more, less or the same once it is warmed up?
I am thinking; if it hesitates less when warm, that would point to a lean condition. If it makes no difference, that may point to timing?

[Bill G]

Originally Posted by Neshkoro

Autolite ASP 3076 Sorry. I forgot to add the part number.
They are from NAPA and the only number they offer.

You can order Champion 3X from NAPA and our store had them in for me to pick up the next day. 3X cost a lot more than the Autolite.

[Neshkoro]

$3.29 vs $7.69 Autolite vs Champion. $32.00 and you're out the door with a set of Champion plugs. Not a big cost difference. Is there a big performance difference? If there is, I'll buy the Champion.

[Neshkoro]

I was looking around at my past posts. I ran across this one about engine stumbling. I got to the part about spark plugs. I started looking on line for plugs. You can get a plug for $5.00 up to $32.00 each. What could make any plug worth $32 when you can get one for $5.00? I know about heat range and that stuff but almost 7 times cost? I suppose if the $32 plug makes your A run better then its worth it but its crazy. I'm not a cheap skate, but still.......tell me why they're better.

[bruceincam]

Originally Posted by Neshkoro

I was looking around at my past posts. I ran across this one about engine stumbling. I got to the part about spark plugs. I started looking on line for plugs. You can get a plug for $5.00 up to $32.00 each. What could make any plug worth $32 when you can get one for $5.00? I know about heat range and that stuff but almost 7 times cost? I suppose if the $32 plug makes your A run better then its worth it but its crazy. I'm not a cheap skate, but still.......tell me why they're better.

Aren't they supposedly the OEM plug? Important to the fine point community I would think.

[Synchro909]

I've always wondered the same thing. I use the Motorcraft TT10) plugs. In fact, I recently changed them for the first time after 45,000 HARD miles. In these engines, plugs should last a lifetime. I think any plug maker that recommends changing at say, 5 or 10 thousand miles is just trying to increase sales and is saying their product is no good.
BTW, the new plugs made no discernible difference.

[CT Jack]

Get rid of the fuel filter. Your carburetor might be warped causing a vacuum
leak at the cover gasket. The carburetor casting where the throttle shaft goes through might be warn causing a vacuum leak. Is your windshield wiper vacuum line sealed? The fuel level in the carburetor might be too low. I would try using a Zenith carburetor to see if your hesitation problem changes.

[CT Jack]

Get rid of the fuel filter. Your carburetor might be warped causing a vacuum
leak at the cover gasket. The carburetor casting where the throttle shaft goes through might be warn causing a vacuum leak. Is your windshield wiper vacuum line sealed? The fuel level in the carburetor might be too low. I would try using a Zenith carburetor to see if your hesitation problem changes.

[katy]

Methinks that the $32 plugs are limited production, that's why the higher price.

[Ernie Vitucci]

Good Morning...I've run Champion W 16 Y plugs for close to 20 years and had good luck with them. They are gaped at 35 thousands and my points are set at 20 thousands. Many A's will tend to want to stall with a quick or panic stop. I have learned over the years to just pull the hand throttle down a little under those sorts of stops. The hand throttle is really a useful tool, if one pays a bit of attention to it...Ernie in Arizona

[Shiloh]

I realize this thread is a bit old but was having the same problem as described and after replacing so many stinking parts I found the problem to be with the fuel flow. Someone had previously used a gasket maker type stuff to try and seal the gas gauge. Little pieces of that had been falling off an partially blocking my fuel flow. I drained the tank. Removed both the valve and fuel lines. Blew everything out with compressed air. Vacuumed what I could out of the tank after letting it sit for a while of course. Put everything back together and it ran great. Then months later started getting a stumble at idle. Got rid of the Tiltson carb and replaced with a Marvel and now it’s purring like a kitten.