What jet size for my setup?

[0101]

My setup is as follows:
2002 400ex
FMF Powercore 4 slip-on
K&N filter
Airbox lid on/off
Dropped a tooth in front sprocket


I ride everywhere from sea level to 8,000 feet in elevation. I usually put the lid on while near sea level and take it off while up in the mountains.

I just found out that I am still using the stock 148 jet (when I bought the bike I was told it was rejetted...stupid liars). I never really noticed any problems with it but now that I have the carb off, I might as well switch it to the proper size.

What size should I use? Ive heard of everything from 150-160.

Any info will be greatly appreciated.

[bigbad400]

no one will be able to tell you one size is gonna work. you need to do a plug check and determine wether its lean or rich. chances are if its running good then you wont need to, lean is a white plug rich is black or carbon built up, good is a light chocolate color almost like caramel. read the jetting thread too that will help alot.

[honda400ex2003]

I would start with a keihin 155 with the lid off, the needle on teh 2rd clip from the top, 38 pilot, 3 turns out on the f/a screw. i ran a 138 dj which is a 150 at 1500 ft with the lid on with my k&n and t-4. you could also try a 158 and see how it is if you are right at sea level. steve