1929 Model A Ford - Engine Intermittent

[82AModelA]

1929 Model A Ford

 

I am in desperate search of a Model A expert... I have a '29 Model A with an issue I can't seem to fix. I need someone more familiar with A's, as I am not - this is the only one I have ever worked with.

 

When the engine is running, it will periodically start running rough - the keyword here is "periodically". I have a clear cap on the distributor and can observe that, during this event of running rough, it is not firing consistently. Also, if it happens to die during this event, it is flooded.

 

However, it is not always running rough. It will usually alternate between running rough for about ten seconds and it will come back around and run perfectly normal. When it is running correctly, it will accelerate perfectly fine and idle fine. In the rough condition, it will struggle to accelerate, and I can make it backfire like a rifle if I get really aggressive with it.

 

The event seems random to me. I cannot cause the event and I cannot make it come out of it.

 

To keep it short, I will say that I have eliminated fuel flow to the carburetor as the problem. I also believe the wiring harness is in order according to the test in the Les Andrews book.

 

Any help is much appreciated. I'm hoping someone might can point out something I'm overlooking. Like I said, I'm not a Model A expert.

Edited October 1, 2023 by 82AModelA
Title not sufficient - no year model (see edit history)

[Oregon Desert model 45]

sounds like distributer is worn.  install new shaft & bushings and that should get it running better.  lots of online suppliers for model A parts to choose from.  tips for removing the old bushings and reinstalling new ones can be found on youtube.  you will need a 1/2" reamer for the bushings after they are installed. 

[WPVT]

You've probably already replaced the condensor. If not, it may be worth trying. A bad one can cause some pretty mystifying symptoms, much like what you've described. 

[82AModelA]

8 minutes ago, WPVT said:

You've probably already replaced the condensor. If not, it may be worth trying. A bad one can cause some pretty mystifying symptoms, much like what you've described. 

Yes I have. I'm running with the modern V8 condensor and points. I've tried three different new condensors and swapped between two new sets of points. Everything came from the same source and I know theres such a thing as bad parts, but its hard for me to believe I would get three bad condensors in a row. I also considered the coil being bad and I changed it - still no difference.

[Oregon Desert model 45]

After having similar intermittent issues, I was suspicious of the new foreign made condensors, so bought a NOS FoMoCo condensor on ebay. It turned out to be slightly longer and I had to drill & tap a new hole in the upper plate for the screw plus elongate the mount hole in the condensor so it would fit - just barely.  After rebuilding the distributor, replacing the condensor, and sealing up the intake manifold vacuum leak, the car starts and runs pretty well now. 

[82AModelA]

12 hours ago, Oregon Desert model 45 said:

After having similar intermittent issues, I was suspicious of the new foreign made condensors, so bought a NOS FoMoCo condensor on ebay. It turned out to be slightly longer and I had to drill & tap a new hole in the upper plate for the screw plus elongate the mount hole in the condensor so it would fit - just barely.  After rebuilding the distributor, replacing the condensor, and sealing up the intake manifold vacuum leak, the car starts and runs pretty well now. 

I've wanted to replace my shaft with a drilled one, so this may be the time. I haven't went that deep into the distributor in hopes that a simple tune up or fixing a broken wire would be the solution. I'll probably look at my distributor before I go any deeper down the condensor rabbit hole.

[WPVT]

21 hours ago, 82AModelA said:

I've wanted to replace my shaft with a drilled one, so this may be the time. I haven't went that deep into the distributor in hopes that a simple tune up or fixing a broken wire would be the solution. I'll probably look at my distributor before I go any deeper down the condensor rabbit hole.

You're taking a good, logical, cautious approach. There is likely one thing causing this problem, not six.

I am not an ignition expert, but wouldn't the capacitance value on a V-8 capacitor be different from that on a 4 cylinder ?  

Here's a suggestion that may be totally off the wall....I was always taught that the purpose of the capacitor was to help avoid having the points get pitted. Try running without the capacitor and see how it runs. I believe an engine will run better without one than with a bad one or the wrong one.  (But maybe I'm wrong )  

Edited October 3, 2023 by WPVT
improved clarity (see edit history)

[82AModelA]

4 hours ago, WPVT said:

You're taking a good, logical, cautious approach. There is likely one thing causing this problem, not six.

I am not an ignition expert, but wouldn't the capacitance value on a V-8 capacitor be different from that on a 4 cylinder ?  

Here's a suggestion that may be totally off the wall....I was always taught that the purpose of the capacitor was to help avoid having the points get pitted. Try running without the capacitor and see how it runs. I believe an engine will run better without one than with a bad one or the wrong one.  (But maybe I'm wrong )  

So the standard capacitance for the original set up - that is original style condensor mounted inside the distributor with the original style points I believe is between 0.20-0.25 microFarads according to Ford, again, that was the setup they had in 1929. For the V8 system...I don't know. I glanced over some articles talking about matching condensors and points, but I felt that was too much info for me. 
 

What I do know is the V8 setup is supposed to work and it is a recommended conversion. I'm just operating under the assumption that the condensor and points I am getting are correct for the intended use as I reasonably trust the parts supplier.

 

I'm actually curious to try running without the condensor just to see what happens. I never really considered what its function was...I just knew it was supposed to have one. I agree with your idea, so long as the point gap is consistent, the engine should fire all of the time for the life of the points.

[WPVT]

1 hour ago, 82AModelA said:

So the standard capacitance for the original set up - that is original style condensor mounted inside the distributor with the original style points I believe is between 0.20-0.25 microFarads according to Ford, again, that was the setup they had in 1929. For the V8 system...I don't know. I glanced over some articles talking about matching condensors and points, but I felt that was too much info for me. 
 

What I do know is the V8 setup is supposed to work and it is a recommended conversion. I'm just operating under the assumption that the condensor and points I am getting are correct for the intended use as I reasonably trust the parts supplier.

 

I'm actually curious to try running without the condensor just to see what happens. I never really considered what its function was...I just knew it was supposed to have one. I agree with your idea, so long as the point gap is consistent, the engine should fire all of the time for the life of the points.

I'm curious to hear what happens. In looking for some component that could operate intermittently, electrical components seem more likely than mechanical components. I've never heard of simply disconnecting the capacitor as a troubleshooting technique, but it seems plausible. 

I did 10 minutes of research and came up with an interesting article chronicling the disassembly and testing of several capacitors, good and bad. Turns out that most capacitors are very cheaply made, and therefore prone to failure. The failure doesn't show up as a short or lack of capacitance, but as high voltage internal arcing due to poor construction. No wonder we've always been taught to replace them along with the points.

[Oldtech]

It should not run worth a hoot without the condenser. The condenser strengthens the spark by storing reverse emf then releasing it as the coil discharges. It also prevents the points burning from arcing.

and No, condensers don't care how many cylinders you have. Most automotive condensers are in that .2 mfd range.

[Bloo]

Bad condensers have been a notorious pattern failure on Model A Fords since the cars were brand new. I don't know why it happens to Model As so much but it does. Whenever there's doubt, try another one.

 

A car will usually not run without a condenser. The spark will be very weak. It might run, but very badly.

 

As @Oldtech mentioned, most condensers are close to the same capacitance. Close, but maybe not the same. Little changes in capacitance do matter, but they do not cause the car not to run. A condenser that is a little off in capacitance will cause short point life due to transfer of metal on the points. You will see a mountain growing on one contact over time. If the capacitance is too small, the mountain builds on one contact, and if the capacitance is too large the mountain grows on the other contact. The driver does not notice any of this until the points are all burned up and causing the engine to run bad.

 

If the points are not growing mountains, a V8 condenser is fine.

 

[WPVT]

I found this article about capacitor failure to be pretty interesting. 

https://nonlintec.com/sprite/cap_failure/

 

 

[wborh37]

Try contacting Paul Shinn (Paul Shinn - YouTube) or Facebook (facebook.com/paulshinn.ford).  His videos have been helpful.

[82AModelA]

So I found my problem. I took a minute and opened up the distributor and checked for side play in the shaft. I found pretty significant play-so much that it would change the point gap by over ten thousandths, so thats not good I'm pretty sure. So I'm going to rebuild my distributor.

 

I'll be rewatching some Paul Shinn videos