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

Re: Engine stumbles on acceleration
 

Take the filter off and try it.

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.

Re: Engine stumbles on acceleration
 

Is your gav set properly? Might be running it lean

Re: Engine stumbles on acceleration
 

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

Re: Engine stumbles on acceleration
 

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

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.

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.

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.

Re: Engine stumbles on acceleration
 

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.

Re: Engine stumbles on acceleration
 

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

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.

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.

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.

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.

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.

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.

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!

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.

Re: Engine stumbles on acceleration
 

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

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.

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.

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!

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

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.

Re: Engine stumbles on acceleration
 

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.

Re: Engine stumbles on acceleration
 

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

Re: Engine stumbles on acceleration
 

Good advice. Thanks for the heads up.

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

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.

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?

Re: Engine stumbles on acceleration
 

Side note: I luv the colour of your ccpu

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.

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.

Re: Engine stumbles on acceleration
 

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

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?

Re: Engine stumbles on acceleration
 

I happen to like my Tillotson.

Re: Engine stumbles on acceleration
 

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

Re: Engine stumbles on acceleration
 

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

Re: Engine stumbles on acceleration
 

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