VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Engine has a stumble when running

Iv'e had this problem for many years and never could find any reason. it always starts and drives anywhere I want but the stumble is quite annoying. I have tried different carburetors and all tune-up parts. I have noticed that it seems to stumble more at night with the headlights on. Does this sound fixable?

Not really unless it does not like the night air....try it in the day time with the lights on.

Timing problem? Do you have it advanced a bit?

I had a problem like yours once. I waited for darkness to see what the problem was. I opened the hood and looked for sparks! Yes, I found that I had bad wire. I could see it in the night but not in the day.

Some quick responses! The timing is set ok but I think there is a bit less pronouncement when the spark is retarded more, also seems less if I set a very small bit of choke. I never have a ping going up steep hills. The idea of night air would be good but it does it more in the daytime too if I turn on the lights, which I try not to do. It never stumbles when pulling or going uphill.

Have you ever thought about changing out the distributor cap. It could have a slight crack in it that gets more open at times depending on heat load.

I have replaced all the distributer parts and pieces, 2 vacuum advance units. different coils, hot wired around switch. I have replaced the carb twice. I am now using a Holly off my old '66 Mustang, Tried 2 Carter W-1 carbs, 2 fuel pumps, now I use an electric. I will start it at night sometime and look in the dark, If I see anything I will be surprised. The wires and all else were new when this car was first run by me after restoration. That is why this problem has been long going and beyond frustration, I just have had to live with it. It can go 65 down the freeway, and climbs all hills around me in Oregon. This problem has remained unchanged all the time I have had the car. The stumble is very light and some passengers don't notice it, but I have to look at my gauges and worry at times especially after dark, when it is more pronounced. Thank you for the replies. J

The fact that the car runs at 65 mph and climbs hills with little effort, to me anyway, rules out the fuel system. With the multitude of parts changes to the ignition system, I'd say you have covered all the bases.

(You mentioned the car was restored, so I'm assuming the wiring harness is "new". But if not.....)

That leaves the wiring, charging system and electrical connections. Those connections under the dash will be tough.

You say it is more pronounced at night....So my questions to you are probably obvious and you have already checked them.........

Have you checked the out put of the generator with the lights on ??

Have you looked at the headlight switch ?? Maybe there is a bad connection that is flirting with ground or an internal problem that may show a black spot on the switch body.

Does the car have a high/low beam switch ?? Check for corrosion at the connections that could be going to ground.

Does the car have a regulator on the firewall or a cut-out switch mounted on the generator ?? Loose connections/poor ground ?? Paint does not make for a good connection.

Are the battery cables the correct size ??

Is the wire between the coil and distributor "new" or is it the original ??

Again these are all things you probably looked at but maybe the questions will have you look at the less obvious.

One last thing to look at which is mechanical not electrical.......How much shaft movement is there in the distributor ?? Excessive movement will cause the point gap to fluctuate .

My generator, with cut out, at the ammeter shows a charge 10 amps and 0 with lights on . The wiring harness and dimmer switch were new as well as plugs and wiring. The distributor was rebuilt to specs. I think I will check my connections one more time with an ohmmeter for good or spurious grounds/opens. I have renewed my search but really appreciate the tips. One my be the culprit. I have all the previous owners (a mechanic) notes.

Keep in mind,just because parts are "New",doesn't mean they can't be defective.

That is a good thought, maybe I will disconnect anything to do with the lighting circuit and see what happens. Thanks

That is what I would do because it "seems more at night with the headlights on." Also, "just because it is a new part doesn't mean it can't be defective." Might be a pinched wire somewhere you have not looked or a loose connection you think is tight that has backed off during driving. Go through the car one part at a time and look under the dash, too. Keep us posted. It will be interesting to see what turns up.