Running rough when hot

[Chris in MA]

Hey all,
Took the 40 out today, runs smooth for about 15 minutes at speed then starts running rough. Stalled at an intersection, cranked fine, plenty of gas, no start. just spun.

Waited about 20 minutes, got it to start, ran smooth at idle/speed for a bit, after a few minutes began running rough again. Pulled over waited about a half hour and drove home. took it easy, but running rough at speed (~30 mph).

back story - just got the car back from the mechanic for a motor refresh recently, have had a few shorter drives, has a fresh Skips coil, rebuilt Bubba distributor, rebuilt carb, new wires. Mechanic said it ran rough with Skips coil. He replaced with NOS coil. I suspect he used the same condenser, but problem he described is similar prior to replacing coil.

If not coil, what else? Seems weird to me that a) Skips coil failed (I have not called him yet to check coil - non issue) AND NOS coil bad?

Your thoughts?

Thanks,
Chris

[ford38v8]

That NOS coil has to go. Skips coil is fresh, NOS is as old as I am.

Condenser good guess, cheap fix. Try that.

Plenty of gas? How would you know plenty? Try pulling off the line from the pump to the carb, then crank (key off) to see if it pumps fuel into a can. May be sucking air not gas.

Rebuilt carb? By who with what parts? Could be bad power valve or poor seal for power valve. New valves have a radius that won't seal to the old carbs. Gotta machine that radius square to get a seal.

So he thinks an NOS coil would be better than Skips? What hole did you excavate to find him?

[mike42]

Chris I had the same problem a couple years ago. I would go with a NAPA condenser that Skip recommended. If that does work have your NOS reworked by Skip and I'm sure your problem will be solved. I had a second coil reworked just to have on hand.

[ford3]

a guess, carb flooding because hear transfer from manifold to carb, put a 1" spacer under carb, aluminum manifolds transfer more heat to carb than cast iron, coil getting hot and breaking down, bad condensor as was stated in above posts, any of those problems will cause your problem, and when the engine cools down it will restart, it could also be the non exestant vapor lock, lol

[Chris in MA]

The carb was swapped as well. Both were rebuilt by Ken a couple of years ago. One was unused and one had been on the car prior to the refresh.

The mechanic is a very reputable local person. I have not spoken to him yet, I just don't think its Skips coil or the NOS coil. At least a lot less likely to be Skips, but if the condenser was not changed, for 12.00 problem solved!

I say its getting gas because the tank is nearly full with fresh gas, and If I look down the carb while cranking I can see gas pumping while the engine cranks.

Going to NAPA...

Thanks.

[36tbird]

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What kind of air cleaner do you have on it?

[Chris in MA]

Original oil bath air cleaner.

[FlatheadTed]

I have never found a NOS coil that's is any good ,first get the skip coil back on it .test drive and check the colour of the spark coming of the HT leads .Blue or yellow .Ted

[TomO]

Check the spark, if it is weak replace the condenser and use Skip's coil.