on my 400 explorerthat i put a hpd pipe with stock scrambler muffler i had to put in a 260 main jet.now i done the homemade airbox mod and i put in the 270 main jet and it missed a little on top end and i checked the plug and it was kind of white so i put in a 280 and it runs better but has a occasional miss in it.the plug looks good with that 280 jet.what should i do???

 

does anyone have any idea??

 

Where is your needle clip set?
up is leaner
down is richer