I know its been discussed a million times but I couldn't come across exactly what I needed.. Iv got a 2002 400ex and I'm running a cobra slip on exhaust and a k&n filter with lid off the box.. So yesterday I took my carb apart because i know I should rejet and a few of the screws had been stripped so I can tell somebody has been in it before, anyway I found that the carb had a k42 pilot and a AB140 main... The bike seemed to be running good but everything iv read suggest I should be running like a 155-165 size jet.. Iv never rejeted before so any insight would be awesome..! I also live in Florida if that's makes a difference!

 

Keihin jets have a k before the number generally. Looks like you have a one size larger than stock pilot. The main is probably aftermarket. The aftermarket numbers don't always correspond to the stock numbers. If it runs well and the plug checks out, I would leave it alone. Sounds like it was jetted after upgrades by the larger pilot.

 

Thanks for the quick response! That's what I was thinking I knew the pilot wasn't stock but iv never seen a main marked AB so wAsnt sure on that and yea it seemed to be running fine all the way to the rev limiter no popping or back firing or anything so it seems ok.. Haven't checked the plug yet though but will soon as I get home