I have a stock 1999 400 EX. My buddy has a 1999 400 EX with the FMF MegaMax II, K&N filter, and jet kit. When we raced last week, I decided to run without an airbox lid and mine was faster than his every time.....even when we switched riders. This week we raced and I had my new K&N filter and was still running without the airbox lid. The only thing he did was clean his K&N. The bikes were dead even and it came down to who got the best start. Do I need to get mine rejetted? Is my mixture too lean? I have ordered the FMF Powerbomb headpipe and FMF PowerCore IV-2 pipe. Should I just run with the lid on until I get them installed and then have it rejetted to run without the lid? Any help or input would be much appreciated.

 

It is best to have your EX rejetted. I live in the Philippines and being in Asia it's warm (90 f). I am currently running 155 main jet with 1 turn in the adjusting screw, 8 pcs. air box vents, K&N filter, Supertrapp IDS2, WB rev, Web Cam 450/451 grind with hardwelded rockers.

 

Get a jet kit it will help with what jet to run where and with what.

99 426ex , Web Cam, FCR carb, CT revlimiter, DMC exhaust, XCT's ,K&N, One kit,

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