I just put on my Dual Yoshimura Pipes and a K&N filteron my 2004 KFX 700 and am thinking it may be a little lean. When you let off the throttle after being at full throttle it will backfire, but small backfires not a loud boom. Is this a carb backfire or a muffler backfire. I dont know the difference. I still have the stock jets in it and live at 5200 feet. The dealer told me that it would be a little rich at this altitude if anything but I was thinking the other way. I am going to pull the plugs and have a look, but if it is lean what size jets do I need to put in? Thanks

 

Do a plug chop. It sounds like you're lean in the idle circuit. If you didn't rejet, you're probably lean throughout. You can probably get away with adjusting the fuel screw, and rejetting the main. Your dealer is probably a retard. Pipes and an air filter, you're gonna need to rejet.