Ok thanks. It was running great till I installed the champion ra8 hc at .033. Was thinking the power commander was trying to compensate for the change. It runs ok but the popping noises makes me wonder. Are new plugs to be tightened beyond the 10 foot pounds to seat the new plugs?First step is to change back to the old plugs that you removed and see if the backfire goes away. If not, then figure out what got messed up when you made the plug change.