My buddy has a k20 that I'm looking at buying. Its got a 350 with aluminum heads, a Comp 4x4 cam, lifters, springs pushrods, longtubes, carb, and I'm sure some other things that I'm missing. The only issue is the motor just doesn't seem to run right. Its got low power and backfires. The cam is flat tappet, and he used stock length pushrods, which is what I think might be the issue. Anyone got an idea what the issue might be?