jetting

[WhiteBros400ex]

i had a 165 in my 400ex with a white brother e series and uni air filter and the plug came out really black but it running ok, i tried a 146 and it runns like crap and the plug is still black any one know what to do ?

thank you

[Holeshot36]

165 to a 146 is a big jump, try going one size down at a time. When i had just a fmf slip on and a uni i ran a 152(148 was stock) and that was perfect.

[cals400ex]

that 165 is quite a bit too big. i assume your using jet kit???? if you are, the 146 is probally pretty close. i think some people even use a 142 with just a pipe. in what way was the bike running like crap with the 146 in??? for the black plug, you could be rich on the mainjet, needle/clip location, or pilotjet/fuel skrew. it could just be an old plug and needs to be replaced too.