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Old 03-26-2021, 05:33 PM   #1
Neshkoro
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Default Engine stumbles on acceleration

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
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Old 03-26-2021, 06:03 PM   #2
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Default Re: Engine stumbles on acceleration

Take the filter off and try it.
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Old 03-26-2021, 06:16 PM   #3
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Default Re: Engine stumbles on acceleration

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.
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Old 03-26-2021, 06:31 PM   #4
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Default Re: Engine stumbles on acceleration

Is your gav set properly? Might be running it lean
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Old 03-26-2021, 06:59 PM   #5
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Old 03-26-2021, 07:32 PM   #6
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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
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Old 03-26-2021, 08:38 PM   #7
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Default Re: Engine stumbles on acceleration

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.
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Old 03-26-2021, 08:48 PM   #8
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Default Re: Engine stumbles on acceleration

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.
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Old 03-26-2021, 08:57 PM   #9
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Default Re: Engine stumbles on acceleration

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.
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Old 03-26-2021, 09:32 PM   #10
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Default Re: Engine stumbles on acceleration

Quote:
Originally Posted by Marshall V. Daut View Post
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.
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Old 03-26-2021, 09:46 PM   #11
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Quote:
Originally Posted by Neshkoro View Post
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.
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Old 03-26-2021, 11:08 PM   #12
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Default Re: Engine stumbles on acceleration

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.

Last edited by ArtimusGordon; 03-26-2021 at 11:13 PM.
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Old 03-27-2021, 07:09 AM   #13
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Default Re: Engine stumbles on acceleration

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.
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Old 03-27-2021, 07:16 PM   #14
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Default Re: Engine stumbles on acceleration

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.
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Old 03-28-2021, 06:06 PM   #15
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Default Re: Engine stumbles on acceleration

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.
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Old 03-28-2021, 07:13 PM   #16
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Default Re: Engine stumbles on acceleration

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.
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Old 03-28-2021, 07:49 PM   #17
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Default Re: Engine stumbles on acceleration

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.
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Old 03-29-2021, 09:16 AM   #18
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Default Re: Engine stumbles on acceleration

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!
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Old 03-29-2021, 10:03 AM   #19
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Default Re: Engine stumbles on acceleration

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.
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Old 03-29-2021, 10:24 AM   #20
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Oh, I missed that detail about the Tilly carb. My suggestion doesn't apply, I think.
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Old 03-29-2021, 11:14 AM   #21
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Default Re: Engine stumbles on acceleration

You may want to consider a rebuilt "Marvel-Schebler" carburetor made to replace the Zenith's for the Model A's.
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Old 03-29-2021, 11:53 AM   #22
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Default Re: Engine stumbles on acceleration

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.
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Old 03-29-2021, 07:02 PM   #23
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Default Re: Engine stumbles on acceleration

Good idea on checking parts. I did rebuild the carb before I did any serious driving. I’m going to check that, too!
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Old 04-10-2021, 11:19 AM   #24
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Default Re: Engine stumbles on acceleration

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
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Old 04-10-2021, 11:34 AM   #25
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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.

Last edited by GeneBob; 04-10-2021 at 11:36 AM. Reason: Add timing pim comment
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Old 04-10-2021, 11:38 AM   #26
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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.
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Old 04-10-2021, 11:51 AM   #27
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Quote:
Originally Posted by Neshkoro View Post
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
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Old 04-10-2021, 03:09 PM   #28
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Default Re: Engine stumbles on acceleration

Good advice. Thanks for the heads up.
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Old 04-10-2021, 04:04 PM   #29
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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
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Old 04-10-2021, 04:36 PM   #30
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Default Re: Engine stumbles on acceleration

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.
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Old 04-11-2021, 12:26 AM   #31
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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?
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Old 04-11-2021, 12:49 AM   #32
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Default Re: Engine stumbles on acceleration

Side note: I luv the colour of your ccpu
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Old 04-12-2021, 08:28 AM   #33
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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.
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Old 04-13-2021, 06:38 PM   #34
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Default Re: Engine stumbles on acceleration

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.
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Old 04-14-2021, 08:08 AM   #35
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I've more or less exhausted all other ideas. That might have to be my last resort.
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Old 04-15-2021, 06:18 PM   #36
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Default Re: Engine stumbles on acceleration

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?
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Old 04-15-2021, 09:58 PM   #37
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I happen to like my Tillotson.
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Old 04-16-2021, 09:19 AM   #38
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Quote:
Originally Posted by Neshkoro View Post
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
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Old 04-16-2021, 11:32 AM   #39
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I saw the spring loaded pin advertised. Maybe I'll buy one. What's another $20.00!
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Old 04-16-2021, 11:27 PM   #40
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If you switched to a modern distributor cap, how are you using the NuRex wrench to set your timing?
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Old 04-17-2021, 05:44 AM   #41
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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?
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Old 04-17-2021, 01:26 PM   #42
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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.
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Old 04-17-2021, 03:21 PM   #43
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Default Re: Engine stumbles on acceleration

I haven’t checked the timing with a timing light. I’ll do that and check back here.
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Old 04-17-2021, 03:33 PM   #44
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If you a vacuum wiper motor check it and the hose for possible leaks.
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Old 04-17-2021, 09:37 PM   #45
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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.

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Old 04-18-2021, 07:11 AM   #46
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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.
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Old 04-19-2021, 08:10 AM   #47
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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.
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Old 04-19-2021, 08:13 AM   #48
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Another good idea. Thanks. I'll try that!
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Old 04-19-2021, 05:47 PM   #49
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Nice thread. Timing is right for me. Thx.
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Old 04-24-2021, 08:54 AM   #50
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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.
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Old 04-26-2021, 07:20 AM   #51
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Default Re: Engine stumbles on acceleration

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!
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Old 04-28-2021, 02:11 PM   #52
BigGameJames
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Join Date: Apr 2021
Posts: 11
Default Re: Engine stumbles on acceleration

Hello all,

New member here.

Looking forward to learning a lot from you all.
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