hey guys. well on my 400ex it runs ok going threw the gears and everything it has a 38 pilot and 148 main jets. if you pull a wheelie and get on the throttle hard from almost no throttle to full it will hesitate a little and wont hold the front end up. it has a fmf power core 4 pipe and that's the only mods. It pops and crackles out the exhaust on deceleration so I thought that meant it was lean. I decided to jet it up to 42 pilot and 155 main jet (stock kehlin not dyno). Still popped on deceleration not as much but it had a terrible bog/hesitation when shifting from gear to gear or getting on it hard. I dropped the main back to normal and it still did it but not as bad. So now I have everything back to stock since i am stumped. Anyone throw in some advice? also when it was hesitating I took the air box cover off and it didn't make any change.

 

Your problem is jetting. Going back to stock is no good. Try a 160 and see if fmf has a recommendation for your set up and elevation.

 

airbox lid on or off?

Also as for pop on decel i would start by backing the air/fuel screw out a bit.

 

Air box lid on. When I jetted up it ran so much worse tho. And now it also smokes once it gets hot and blows oil out the exhaust.