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Fuel problem or ignition problem

Car #4

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Ontario
I took the 68 Charger out for the first time yesterday. 440 with MSD. After about 20 minutes of highway driving to get to town it stumbled, I feathered the gas, it recovered and I drove in town for about another 10 minutes. Then it stumbled again and I was feathering the gas but it died and wouldn't start. Called a tow truck and while waiting I thought I'd try it. It would fire up and die and not fire up again. After five or ten minutes I tried again and same thing. This happened 3 or 4 times, but the car would not start. The tow truck brings the car home and puts it in the shop. A while later, at least two hours after it initially died, I tried and it started right up and ran fine for a minute until I shut it off.
This engine was rebuilt about 4000 miles ago and has an Edelbrock top end kit on it, cam intake heads and carb. My mind at first went to ignition problem because when I bought the car I had a lot of running issues which got resolved when I replaced the MSD box with a new one. It hasn't missed a beat since.
A couple buddies are thinking it's fuel related. But I've never had fuel issues before. One suggestion was that the tank isn't venting properly creating a vacuum but that's never happened before so why now? Fuel pump? But it's a new pump 4000 miles ago.
Your thought's please.
 
Could be a worn fuel pump push rod. Was it replaced when the fuel pump was ??
 
look down the carb, do you see fuel if you pump the throttle? if not fuel problem. pull the coil wire, crank the engine, is there spark? if not, spark problem. you need to do some tests to find the issue.
 
Fuel pump rod
Fuel floats set too low
Fuel tank screen plugged
Fuel filter plugged
Bad gas

How old is the tank? How old is the gas?
 
I had this identical problem with my '62 Imperial from Arizona. Turned out to be a bad coil that would work fine until it got hot, one of the few items not replaced when I had a complete engine overhaul. Shut the car down, and it would run fine after it cooled off, then stumble after it got warmed up.
 
Fuel is from last fill up in November of last year treated with Stabil. That’s my normal process, never had an issue. Plus I have 4 other vehicles with last fall’s gas that have been problem free.
Don’t know if fuel pump rod was replaced when engine was rebuilt. I bought the car done.
 
I would try and duplicate at home. Maybe run for 20-30 minutes at 2000 rpm and see what happens. If you can repeat it check for fuel and spark.
 
It started up and ran fine again today. I could carry a spare coil and swap them if it happens again. That would test the coil.
 
I'd start by checking for spark when it doesn't start. Easiest test there is.
Doug
 
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