i only know what i learned here...
plus i am in the middle of rebuilding my 400 so i know a little more about them thanks to
the guys on here..

 

Does it have a factory silencer on it???I had a 86 250r quad that did that and the silencer was clogged.so I tooked out the screws and ran it cleared up

 

Raise your needle by lowering the e-clip before you have to replace another piston. You may also need to go larger with your main jet which is easy to do also. Turn your carb over and take out the plug on the bottom of the bowl, using a 6mm socket unscrew the little brass jet, it will have a number stamped on it, the bigger the number the more fuel it will flow. the main jet controls fuel flow at 3/4 to wide open, the needle is for 1/4 to 3/4, although they do overlap some.