I just received my 450/451 webcam for my 400ex. I currently have my machine jetted correctly for my previous modifications done last year (still using my stock cam).

Does anyone have experience with jetting changes that may occur when just upgrading the cam? If so, what changes were made?

Thanks for your help,
ogre

 

You typically have to go larger on the main.

For instance - 2 identical bikes (mine and a buddy) - the only difference:

Mine - XR Cam - likes a 168-170 main & LOTS of accelerator pump

Friend's - GT Thunder cam - Likes a 178-180 & less accelerator pump

Pilot jets are very close on these 2 bikes.

One point of note, the cammed 400's like a very free flowing exhaust. Fueling demands are much more linear with a free flowing silencer. A restrictive silencer may make it impossible to tune the low end without being so lean on top that you're melting pistons. Shoot me an e-mail for a more detailed discussion...

 

Gabe,

My motor was just put back together a few days ago after having my modifications to the motor done. I had an 11:1 compression piston and an XR400 camshaft installed. I have an FMF Power Core IV-2 silencer as well. A while back when I bought my silencer, I bought a Dynojet kit. The biggest mainjet in the kit was a 170. With this main installed, the bike still ran a little lean. The guy building my motor didn't have anything bigger in his shop, so he called Dynojet to order something bigger. He order everything from a 175 up to the biggest, which is a 210. He said that he'll have the right one for mine, plus extras. Do you think at my elevation (about 350-450 ft. above sea level, depending on the track), with my modifications, that this jetting (above a 170 main) is correct? Or do I have some sort of leak somewhere? I doubt it, but just thought I'd ask. You seem to know a LOT about these bikes, so I thought I'd ask for your help. Any assistance you can offer is greatly appreciated. Thanks.