just a dirty carb or what?

[GMC400ex]

ok so i just got this 03 400ex and the guy bought off another guy who never ran it...since 04 he said hes maybe ran two tanks of gas through it..i jetted it bc it has an FMF exhaust and i put a 155 in it bc 148 was stock and only jets i had were a 150 then a 155 you think a 150 would be better? but the MAIN problem is the back firing which im sure is where it is lean and the baffle is out of the exhaust and it will never ever idle...it will idle real nicely on full choke..idle kind of high on half choke and completely die on no choke..so do you guys think i just need to clean the carb real good and adjust the idle screw and the fuel/air screw? any suggestions would be greatly appreicated..im dying to get this thing running right..

[rob_990]

id try cleaning the carb and putting in a 42 pilot jet

[Honda#4]

I'd up the pilot to a 42 like Rob said and run through all the carb circuits to see how they all feel. If you just have a pipe and maybe a filter the main might be ok but you gotta check for sure.

[GMC400ex]

ok so i went through a completely cleaned every bit of the carb my fuel/air screw was packed w/ old fuel and the hole was just as dirty..i also changed my needle to the 4th setting like the jet kit said..but i am still having the same problem..no idle..adjusted the idle screw and all but this time my headers started glowing orange..what the hell is going on? its still running lean and backfiring.. and i have a really stupid question..but id rather look stupid asking than look stupid trying to act like i know what im talking about haha but you guys discuss adjusting the pilot jet to a 42..how do i do that..i have a jet kit and its an FMF jet kit and mentions nothing of a pilot jet or nothing could you explain on how i could about doing that to maybe help this problem get fixed..i greatly appreciate any suggestions

[matt14c]

Your pilot is next to the main jet when you have the bowl off the bottom of the carb. If your head pipes are glowing then your too lean. With that FMF did you get a dyno jet kit or are there keihn jets in it? If there dynojet then the numbers are different then the keihn and im not sure where you would have to be. Also for jetting if you look through the stickys at the top of the page it will answer all your questions and then some. Welcome to the site and good luck.

[mcgrath]

heh GMC I would put the needle back in the third clip, you put it in the 4th but is that from the top or bottom? You can get a new pilot jet from your local shop. Id get a 40 and 42. With a 155main and a 40-42 pilot and the needle in the third clip(middle). You should be pretty good. If you moved the clip up one notch you would have leaned it out even more. The jetting I told you is a pretty standard starting point. Good luck.

[GMC400ex]

hey thanks guys for all the help i am working on cleaning the pilot jet and adjusting everything..i just havent had time to do it all..im actually in class now haha..but thanks for suggestion and i am SURE ill need your guys assistance and im excited to get riding

[mitchamus]

make sure you plug is good too, prolly has nothing to do with it but cant hurt.