I did not understand well, but a guy posted that he needed to loosen his rockers, and turn them in a bit at a time (so not to kill it ) to get his lifters to bleed down??? Anyway """popping in the airbox, and backfiring""" sounds like valves. Idk, Idk, Idk. What he was describing is the same as what you get adjusting the lifters on an old chevy, It misses as you go down. In any case, you can't turn a push-rod under pressure.