Ok, again I have troubles with this friggin engine! It's the 4.3L V6 in my '86 C10. I built the motor last fall, it now has 8000mi on it. This is a great problem, that has me pissed and intrigued at the same time. More pissed than anything else. What the truck does now, and this just started 2 weeks ago, I start it runs great. Truck wamrs to operating temperature, and starts cutting out, dumping gas into the exhaust, the thing spits, pops, backfires midly and violently, out the exhaust, does that for 2-3 minutes, trucks runs perfect for the rest of the day, or until it gets cold again. I have no emmissions, it has a holley 390cfm carb on it, I've had the HEI module checked, I disabled the ESC with disconnecting the sensor, then disconnecting the harness at the distributor and jumping pins a & c so it runs. Still it does it,so its not ESC. Plugs are new, wires are new, plugs are nice light brown color. Could this be a carb problem? Blown power valve? It's either not getting spark, or just way too much gas, but only at the point it reaches operating temp? It's seems to be getting worse too. It started just a couple little pops and whatnot, now it's to the point where I don't think it's going to make it next time. I ran compression and leakdown on all cylinders, 175psi +-3, and 8% leakdown on all of them. So I don't think its and internal engine problem. This is really ticking me off......I'm going to pull it in the garage tommorow and start checking things out, again. Just thought I see if anybody has an opinion on what this is.