I have a problem. I can fire up my car and go for a cruise, no problems. It will idle @ 1200 in neutral and 1050 in drive, no problems at all. About 45 min of cruising, it won't idle woth a crap, it won't idle at a stop light and it sometimes stalls and backfires through the carb. Outside temps about 85 deg F, engine temps never get above 180 deg. I shut it down for 1/2 hr, carry on cruising and everthing is fine for another 45 min or so, then idle turns to crap again. Carb is a Holley 750 DP, mech secondaries and choke. Ignition is a Pertronics HEI, all MSD wires. I probably shoulden't worry to much about it, next week I am putting on a new Holley 850 DP, and all new MSD (6AL and billit distributer), but it bugs me why this is happening.
Cheers
Bear

You could have a coil that is overheating. Im not familiar with this HEI but if it uses less than 12V check to make sure that during the run mode that it is getting correct voltage, You could also have problems with voltage regulation if the system is putting out too much voltage you could be doing the same thing with overv heating the coil. Get some specs from the manufacture/manual and check your resisitances on the coil terminals to make sure you are within specs.