I'm having a problem with the car, and I need some help with a possible diagnosis. I went to the track yesterday for a two day race, and the car ran great all day, but then this morning on the first time run, the car broke up really bad and almost died, I thought maybe a plug wire was off, so I checked & the wires were fine, I pulled the front and rear bowls off to check for trash, I found a couple of very small pieces, so I thought maybe that was the problem, so I went up for the next time shot and the car almost died when I hit the gas and would barely run under any amount of throttle. talked to a knowledgeable local engine builder, & he suggested we check for a broken valve spring, we did, and they were all OK. I loaded up and came home, changed the plugs which were old, an that didn't help much either, I have a temp gun, so I went around and checked all of the headers and I found that #4 & #6 are cold and apparrently not firing. Question is what else should I check, the plug wires look OK from the outside, so what is the next thing to check?