Not sure on internals, since I bought the motor 10 yrs. ago, but it is by no means radical. Anyway, motor is in 70 dart with points dist. 727 and 3:91 suregrip. Went to Street machines and done a few burnouts in the campground, as it will light the tires instantly. All was fine until it wouldn't even turn a tire over. I had literally just lit the tires, went around a corner and tried to do another, and it fell on its face. Twice. Ran fine rest of the weekend until the drive home. Got on the Istate after about 20 miles of 2 lane or so, got up to 55 or 60 for a mile or two and it starts popping, backfiring and acting like its out of fuel. Pull off to the side and it finally clears up and will rev. Pull back out and it does the same thing 4 more times. Ended up swapping it out in the trailer with a buddys car. get it home, and wont do a burnout. tried 4 or 5 times. 5 minutes later was driving it home, stopped, and it instantly lit the tires like nothing was wrong. Week later, thinking I had bad gas, drained tank put in 93 octane, and now, it wont idle. Always idled about 1000 rpm in park, 5 to 700 in gear. Now its 7 to 800 in park and 3 to 400 in gear. Hadn't touched timing or idle screw, Bump the timing up and idles better in park but still the same in gear. Pulled the plugs, they looked good. Put in a new set just because, and voila, it idled fine. So down the road for a run test, and it ran better than it ever had. All of a sudden when I pull up to a stop sign, it wont idle again. Is this all related or is this multiple problems? Pulling my hair out, somebody give me some help please.