I just put a HMF slip on and K&N filter on a completely stock 06 650 Brute Force today. It runs really well but pops a lot on deceleration. I've had atv's that have done this in the past, but it seems excessive. I went with 145-148 which is a little bigger than what HMF recommended. I read where popping could be a lean condition so I went to 148-150 and the pops got worse. I haven't messed with needle setting, pilots, or the fuel/air screw becasue I didn't see it anywhere on the bottom of the carbs. I looked at the plugs and they were pure white and looked a little lean, but going up made it worse so I'm confused. I've got a DS650 with a big lectron carb, but this 4×4 is kicking my butt! Any help would be appreciated.

 

This was happening to me after i put my muzzy system on. Turns out the cvt intake pipe wasnt connected to the airbox so i was sucking in way too much air.

I would suggest going up on your pilots and maybe shimming your needles.