Stalling and backfiring after driving 50 min

[REByar]

If I drive around town and keep the speed at 40 or less everything is fine no matter how long I drive. But if I want to drive to the next town, approx. 45 miles away, and drive for most of the drive over 45mph after about 50 min the car starts to sputter and backfire and the more I press the gas pedal the slower the car will go. If I can nurse it along for about 3-4 min all of a sudden it will start to run fine. If I pull it over, which I did the first two times it happened, the engine will die. It will then not start. I will pull out one of the plugs and it is covered with carbon. I will try and start it again and it will not start. The first time it happened I had to have it towed. The second time I pulled over I had to let it cool and then cleaned off the plugs. It would then start again. If it occurs and I can nurse it along and it starts to run fine again I can make it to the next town. But when I leave I can drive for about 50 min and it happens again. Any ideas what is happening? Any advice would be greatly appreciated.
Thanks
REB

[Mitch//pa]

Link to his other thread with more info
https://fordbarn.com/forum/showthread.php?t=215518

[eagle]

You have to isolate the problem first to either electrical or fuel. Contrary to most of the advice you're about to get I would recommend NOT starting by replacing parts. One quick test, does pulling the choke or adjusting the gav make any difference? Also pull a couple spark plug wires just off the plug top and check for nice hot spark. Check for proper point gap. Are you running an air filter? If so try without. I run one but you have to keep it clean, some cars can't handle them at all. Where are you running the timing? I run mine as low as i can without pinging. If you're plugs are truly fouling that's a problem, or is it that sitting while you clean them is what is "fixing" it? Check gas tank vent too. Get back to us with results.

[jm29henry]

Good trouble shooting is the most important thing you can do and you don't want to spend money on new parts that you don't need !.However I don't know how to test a condensor ,but if you have a spare one I would try it . I also had a bug similar to yours it ran great cold and the warmer it got the worst it ran.as a last resort ,I tried a new condenser at it was all I. Needed .I ask the question at my car club meeting and I was told that some condensor don't totally blow and will still operate poorly.

[joncrane]

I had a very similar situation in my '28 pickup. I suspected a carburetor issue, but after it failed I mistakenly brushed my arm against the coil. It was hotter than a two dollar pistol!
Replaced the coil and never had another problem again. Apparently the coil would heat up over time, ie some sort of short. When cold the car started and ran perfectly. After running 20 minutes or so, sputter, miss, and eventual shut down.

[Tom Wesenberg]

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As soon as the engine starts to die, get out and hold the coil wire 1/4" from a head nut to check for a hot blue spark. If it's good, then look at the fuel supply.

It sounds like it runs low on fuel to me. Remove the fuel line at the carb, see how far the lone extends beyond the ferrule. It should be no more than about 1/8", or it may hit the filter screen and block off some flow. Let the fuel flow into a quart jar to see that it can maintain a good strong flow for several minutes.

If the flow checks out, then take the carb apart to check the filter screen, jets, and passages. If you have a known good carb to swap, that would be a quick easy way to know also.