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

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
 
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
 
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.
 
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?
 
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.
 
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.
 
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?
 
You must log in or register to reply here.
Back
Top