Rough running/starting when warm

[W4ATL]

My '68 Charger with a 440 started developing a nagging problem where it would be hard to start after it was warm. If I immediately cranked it back up after a warm up it would start but if I let it sit for 2 hours it wouldn't start. When I finally got it cranked it ran rough for a while and then started to run OK. Finally, it got to the point where it wouldn't run very well at all.

It appeared to be getting spark. I had not been through the carb since I bought the car so I took the carb off, cleaned it and used a re-build kit. I was concerned since the carb actually looked pretty good. I put it back on the car and it wouldn't start at all. It was at this point that I remembered having to replace the coil about 3 years ago when I first got the car because it just wasn't running right. My mechanic at the time swapped the coil and that solved the problem.

So, on a whim I ordered a new coil and it fixed the problem! Cranks right up and runs great hot or cold.

I am perplexed about why the coils keep going out. The car uses a chrome electronic ignition box with dual ballast resistors. I checked the wiring and the 5 ohm and 1 ohm sides of the ballast resistor are wired to the coil right. It is mounted in the standard location next to the carb under the air filter.

Anyone out there with some ideas?

[elacruze]

What coil and ballast are you using?

The chrome box should have P2444641 1/4 ohm ballast and 4876733 coil.

[W4ATL]

I just ordered and installed the UC12X Standard coil. Not sure of the part number of the ballast resistor but one side reads 5 ohms and the other side about 1 ohm. The new one I just bought reads identical so it went in my spare parts toolbox in the trunk.

[elacruze]

I don't have all the information to do the math on all the parts but if you're running on 5 Ohms when you should have .5 Ohms you could simply be overcurrenting the coil and overheating it.

[W4ATL]

I don't have all the information to do the math on all the parts but if you're running on 5 Ohms when you should have .5 Ohms you could simply be overcurrenting the coil and overheating it.

I checked and the resistor is wired with the proper resistances going to the proper places. The only thing I can think of is it is getting hot mounted on the engine. I moved it a bit forward out from under the air filter to see if that will help.