39 fcr carb jetting help

[shawn1103]

i just bought my 05 400ex and i have added the following:

- scorpion full race exhaust system (love it!)
- k&n air filter
- k&n air box lid
- keihin 39 fcr carb.

i bought the carb. slightly used and i cant seem to get it to function right. it is hesitating really bad when i give it full throttle and when your riding it, it cuts out at high rpm. i have an assortment of main jets that i keep trying, from 155 to 170 and none of them do anything different. i tried changing the e-clip on the needle and that made a little difference. can anyone help?

[cals400ex]

make sure both air boots are on snug and tight and neither have any cracks in them. then i would start with around a keihin 165 mainjet, needle clip in 4th position from the top, and a 52 pilot jet. the missing at low rpms when you nail it is from that damn accelerator pump. it quirts gas way too long. get the rpms up a bit or ease into the throttle for a bit until the rpms do increase. you can rig that accelerator pump but i never had perfect success doing that.

[shawn1103]

where does the pilot jet go, and what does it do?

[cals400ex]

the pilot jet mainly affects the air fuel ratio from idle to 1/8 throttle or so. i ran a 50 pilot jet and that was ok. you can probably go one way or another a size or two and still be able to run find. it is right next to the mainjet.