why am i running lean?

[bone705]

not to long ago i put a hi comp piston, #236 Web cam, k&n, and fmf exhaust on my 300ex. i installed a 135 main and 40 piolit. I had the air screw adjusted were the plugged look like it was burning good. I rode for about month and then all of a sudden its running lean. Ive screwed the air screw out a half turn and its still lean. i also checked the air boots and they all looked fine. what would casue it to get so lean? and what do i need to do?

[Evan400ex]

It is your main jet probably. I know you have a 300 but I run a 165 main in my 400. With the mods you have I would go up a few sizes on the main.:macho

[cals400ex]

list off the sizes of the stock jets on a 300ex, i only know about the 400ex factory jet sizes.

[44oEX]

It's not your main jet my friend runs a 128 with the same stuff but no cam.

It is either that your main jet is dirty or your filter is dirty try cleaning out the carb and filter and see what happens.