You are running rich. Cool air is more condensed and thus packs more 'bang' (hp) when ignighted. Go back to 42's and check the idle mixture screws. you should be about 2-3 turns out from full stop. As for the popping, look for exhaust leaks. Torque the header falnge bolts and look where the silencers hook up to the header pipe. I'd bet you have a leak...
