Ignition or fuel issue?

[John in KY]

Hi all,

It’s been quite a few years since I’ve posted to the forum. Being that my Cub had been running perfectly and never giving any trouble I’ve not found my way here in a while. But recently my Cub has done something out of character and decided to frustrate me. My Cub is a ’69 12volt with distributor and hydraulics. My grandfather got it new and took good care of it. I’ve had it 8 or 9 years. It has always run extremely well and started so easy it was spooky. Just close the choke lever at the carb, then just a quick tap the starter button and it would instantly start, then turn off the choke. (I’m talking about the lever at the carb, not the seat operated choke control) Same thing if hot but no choke required. After starting she would then run perfectly with no hesitations, misses, or anything.

But beginning a few months ago after it would get warmed up the engine would die instantly with no sputtering or anything preceding. Just like I had turned the switch off. And then it would start right back up and run perfectly again for a few minutes before doing it again. It would always start right back and run perfectly until the next time it died and each time it would seem to die a little sooner than it did the previous time. I decided it was something breaking down in the ignition system and instead of trouble shooting the specific problem I decided to completely rebuild the system. New coil, points, plugs, plug wires, condenser, distributor cap, and rotor. Timing has been carefully set and re-checked. And now?

Now it starts but not nearly as easily as it did before. And now it will not run without the choke lever staying almost fully on. After it starts I turn the carb choke lever back just a tiny bit and then the engine runs perfectly. Pretty much just as it did before except it cranks a bit before starting and the choke must stay almost fully on. This is starting to sound like a fuel issue now, but I’m pretty sure it was dying before due to a heat related ignition issue.

So any thoughts? Do I now have a fuel related issue unrelated to the ignition problem? I don’t like coincidences like that but I’ve certainly seen stranger things. Or did I have both all along, but it seemed to run perfectly before. Or did I mis-diagnose the problem to begin with, but the dying certainly seemed ignition related to me. Or am I overlooking an ignition related issue that could account for these problems? I could probably go out and use the Cub as it is because it does run fine with the choke on but it goes against everything I believe to operate it when I know something isn’t quite right.

So any thoughts?

John Davidson
’69 Cub
’46 Farmall A
A few military vehicles, and a couple old planes...

[bob in CT]

Sounds like 2 problems. Hot shutdowns are frequently because of a bad coil. Works fine when cold and croaks when hot. Perhaps this was fixed with the new coil.

Your fuel issue sounds simple too, hopefully it is. There is a brass nut on the side of the carb. Shut off the fuel, loosen and remove the main jet and see if it is clogged. A fine strand of copper telephone wire is ideal and some compressed air.

Here is a photo of the nut, thanks to TM Tractor. It is at the bottom of the bowl on the side:

[Eugene]

No disagreement with Bob. Sounds like fuel flow and coil break down.

Finish the complete tune up including compression tests and valve tappet adjustment. Triple check ignition timing. Then the carburetion issue. Lastly, before spending money, swap out the coil with a known good one.

[John in KY]

Thanks for the quick replies. I'll check the main jet and finish up the tune up with the valve tappet adjustments etc. I've probably checked the timing 10 times and I think that's good, but I'll check it again. I think the ignition problem is likely fixed as it hasn't died since I went through it, that is except for when I turned off the choke. The only difficulty in the ignition system tune up was the points gap. I've never had so much difficulty setting the gap on a vehicle in my life. Tighten it once it gets narrower, tighten it the next time it gets wider. I finally got it right on the money but i'm glad no one was around to hear me. But none of that was anything compared to my decision widen the track of the front axle one notch to optimize it for my 193 plow. It had been where it was since it left the dealer in '69 and it had no intention of changing. But that's another story. I'm out plying the skies across the country for the next week or so, but soon as I get home next week I'll get right on it and let you all know what I find. Thanks again so much for the help.

John Davidson
’69 Cub
’46 Farmall A
A few military vehicles, and a couple old planes...