jet size?????

[pauls400ex]

i have a 2005 400ex and instead of just buying a jet kit and wasting money, wat size does the jet have to be because i'm going to pipe it and get k & n for it

[atvracer980]

Rule of thumb, upgrade the exhaust and air filter- go up 2 sizes on the main jet, if its running a 142 main jet, 2 sizes would be in the ball park of a 148 main jet- the jets usually run in a 3 number spacing ie: 135, 138, 142, 145, 148 ect.- hope to help ya out.

[jsmith2232]

I had a 146 dynojet main in mine with just afilter, revbox and pipe and it was perfect.