OK,i was running K and N filters on my 91 banshee,with no air box,i also run an old DG (i think) 2 into 1 exhaust,so it comes out the back as a single exhaust.I wanted to switch back to a regular stock airbox,because i ride in a lot of mud and water.So i put on my new banshee stock airbox and filter,and now the banshee wont rev out.If i take the lid off of the air filter box,it runs fine.I messed with the air screws a bit(that didnt help)---So with the airbox lid on im not geting anough air. Right now im running a 25 pilot,and a 290 main jet. What should i change jetting wise to correct this problem. maybe a smaller main? like a 260?

 

You are starving the motor for oxygen, so you will need to go down on the main jet by at least 2 jet sizes (would be my guess). move the needle clip UP one notch, and you may or may not also have to go down a size on the pilot jet.

Be sure to do a plug check with a fresh white plug after doing these jetting changes.

I would start out there and see how that affects it.

 

Thanks,i ride a lt250 myself.My girlfriend rides the shee,it ran really nice with the k and n's on it,but i couldnt get her to stay out of the water or mud,and i dont want to be rebuilding it.It ran great without that lid on.Ill try that advice today

 

Ya, your defenetly to high on the main jet. your pilot should be fine. If you never changed your needle position then I would leave it alone unless your jetting/air mixture is a hair off after rejetting down.