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03-26-2021, 05:33 PM | #1 |
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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 |
03-26-2021, 06:03 PM | #2 |
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Re: Engine stumbles on acceleration
Take the filter off and try it.
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03-26-2021, 06:16 PM | #3 |
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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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03-26-2021, 06:31 PM | #4 |
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Re: Engine stumbles on acceleration
Is your gav set properly? Might be running it lean
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03-26-2021, 06:59 PM | #5 |
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Re: Engine stumbles on acceleration
Check your "Private Messages" in the top right corner of this webpage.
Marshall |
03-26-2021, 07:32 PM | #6 |
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Re: Engine stumbles on acceleration
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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 |
03-26-2021, 08:38 PM | #7 |
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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. |
03-26-2021, 08:48 PM | #8 |
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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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03-26-2021, 08:57 PM | #9 |
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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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03-26-2021, 09:32 PM | #10 | |
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Re: Engine stumbles on acceleration
Quote:
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03-26-2021, 09:46 PM | #11 |
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Re: Engine stumbles on acceleration
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03-26-2021, 11:08 PM | #12 |
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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. |
03-27-2021, 07:09 AM | #13 |
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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. |
03-27-2021, 07:16 PM | #14 |
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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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03-28-2021, 06:06 PM | #15 |
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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. |
03-28-2021, 07:13 PM | #16 |
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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. |
03-28-2021, 07:49 PM | #17 |
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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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03-29-2021, 09:16 AM | #18 |
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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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03-29-2021, 10:03 AM | #19 |
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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. |
03-29-2021, 10:24 AM | #20 |
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Re: Engine stumbles on acceleration
Oh, I missed that detail about the Tilly carb. My suggestion doesn't apply, I think.
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03-29-2021, 11:14 AM | #21 |
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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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03-29-2021, 11:53 AM | #22 |
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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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03-29-2021, 07:02 PM | #23 |
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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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04-10-2021, 11:19 AM | #24 |
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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 |
04-10-2021, 11:34 AM | #25 |
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Re: Engine stumbles on acceleration
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 |
04-10-2021, 11:38 AM | #26 |
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Re: Engine stumbles on acceleration
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04-10-2021, 11:51 AM | #27 | |
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Re: Engine stumbles on acceleration
Quote:
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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04-10-2021, 03:09 PM | #28 |
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Re: Engine stumbles on acceleration
Good advice. Thanks for the heads up.
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04-10-2021, 04:04 PM | #29 |
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Re: Engine stumbles on acceleration
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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04-10-2021, 04:36 PM | #30 |
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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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04-11-2021, 12:26 AM | #31 |
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Re: Engine stumbles on acceleration
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? |
04-11-2021, 12:49 AM | #32 |
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Re: Engine stumbles on acceleration
Side note: I luv the colour of your ccpu
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04-12-2021, 08:28 AM | #33 |
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Re: Engine stumbles on acceleration
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. |
04-13-2021, 06:38 PM | #34 |
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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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04-14-2021, 08:08 AM | #35 |
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Re: Engine stumbles on acceleration
I've more or less exhausted all other ideas. That might have to be my last resort.
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04-15-2021, 06:18 PM | #36 |
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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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04-15-2021, 09:58 PM | #37 |
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Re: Engine stumbles on acceleration
I happen to like my Tillotson.
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04-16-2021, 09:19 AM | #38 | |
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Re: Engine stumbles on acceleration
Quote:
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04-16-2021, 11:32 AM | #39 |
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Re: Engine stumbles on acceleration
I saw the spring loaded pin advertised. Maybe I'll buy one. What's another $20.00!
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04-16-2021, 11:27 PM | #40 |
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Re: Engine stumbles on acceleration
If you switched to a modern distributor cap, how are you using the NuRex wrench to set your timing?
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04-17-2021, 05:44 AM | #41 |
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Re: Engine stumbles on acceleration
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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04-17-2021, 01:26 PM | #42 |
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Re: Engine stumbles on acceleration
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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04-17-2021, 03:21 PM | #43 |
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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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04-17-2021, 03:33 PM | #44 |
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Re: Engine stumbles on acceleration
If you a vacuum wiper motor check it and the hose for possible leaks.
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04-17-2021, 09:37 PM | #45 | |
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Re: Engine stumbles on acceleration
Quote:
John |
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04-18-2021, 07:11 AM | #46 |
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Re: Engine stumbles on acceleration
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Thanks for the ideas. |
04-19-2021, 08:10 AM | #47 |
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Re: Engine stumbles on acceleration
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. |
04-19-2021, 08:13 AM | #48 |
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Re: Engine stumbles on acceleration
Another good idea. Thanks. I'll try that!
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04-19-2021, 05:47 PM | #49 |
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Re: Engine stumbles on acceleration
Nice thread. Timing is right for me. Thx.
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04-24-2021, 08:54 AM | #50 |
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Re: Engine stumbles on acceleration
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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04-26-2021, 07:20 AM | #51 |
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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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04-28-2021, 02:11 PM | #52 |
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Re: Engine stumbles on acceleration
Hello all,
New member here. Looking forward to learning a lot from you all. |
05-10-2021, 08:16 AM | #53 |
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Re: Engine stumbles on acceleration
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 |
05-10-2021, 09:34 AM | #54 | ||
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Re: Engine stumbles on acceleration
Quote:
Quote:
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05-10-2021, 10:30 AM | #55 |
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Re: Engine stumbles on acceleration
What spark plugs did you use? What did you gap them at?
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05-10-2021, 04:18 PM | #56 |
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Re: Engine stumbles on acceleration
.035 and Champion plugs, if I remember.
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05-10-2021, 07:15 PM | #57 |
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Re: Engine stumbles on acceleration
My sometimes does stumble on accel. I adjust the GAV to let more gas in. Cures the stumble.
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05-11-2021, 09:58 AM | #58 |
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Re: Engine stumbles on acceleration
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! |
05-11-2021, 11:10 AM | #59 |
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Re: Engine stumbles on acceleration
Set your plugs to .025 on a 6v system - try that. .035 is pretty wide.
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05-12-2021, 05:48 AM | #60 |
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Re: Engine stumbles on acceleration
I’ll try that.
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05-12-2021, 11:26 AM | #61 | |
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Re: Engine stumbles on acceleration
Quote:
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05-12-2021, 11:45 AM | #62 |
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Re: Engine stumbles on acceleration
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!)
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05-19-2021, 06:42 PM | #63 |
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Re: Engine stumbles on acceleration
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. |
05-20-2021, 09:56 AM | #64 | |
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Re: Engine stumbles on acceleration
Quote:
Saying that the plugs are Autolite is like saying the car is a Ford or whatever. What number are the plugs?
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05-20-2021, 10:57 AM | #65 |
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Re: Engine stumbles on acceleration
Autolite ASP 3076 Sorry. I forgot to add the part number.
They are from NAPA and the only number they offer. |
05-20-2021, 01:19 PM | #66 |
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Re: Engine stumbles on acceleration
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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? |
05-20-2021, 05:41 PM | #67 |
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Re: Engine stumbles on acceleration
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05-20-2021, 05:49 PM | #68 |
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Re: Engine stumbles on acceleration
$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.
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03-09-2022, 06:38 PM | #69 |
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Re: Engine stumbles on acceleration
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.
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03-09-2022, 06:50 PM | #70 | |
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Re: Engine stumbles on acceleration
Quote:
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03-09-2022, 08:39 PM | #71 |
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Re: Engine stumbles on acceleration
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.
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03-09-2022, 11:10 PM | #72 |
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Re: Engine stumbles on acceleration
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. |
03-09-2022, 11:13 PM | #73 |
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Join Date: May 2010
Location: Hebron, CT
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Re: Engine stumbles on acceleration
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. |
03-10-2022, 10:53 AM | #74 |
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Re: Engine stumbles on acceleration
Methinks that the $32 plugs are limited production, that's why the higher price.
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03-10-2022, 12:48 PM | #75 |
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Re: Engine stumbles on acceleration
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
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01-30-2023, 02:19 PM | #76 |
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Location: Lowell, Arkansas
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Re: Engine stumbles on acceleration
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.
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