Need help jetting a 426 in Pueblo Colorado

I just bought a 00' YZ426F. It came from Arizona & I live in Pueblo Co. I took the carb apart, cleaned it & put it back together. It started extremelly hard, but once it did start it idles smooth & is responsive except for a litttle bog at low RPM. Should I re-jet or do the AP upgrade & see how it likes that first? Its stock on jets & needle clip position. Any help will be greatly appreciated, Thanks. Also elevation is about 4700'

The '00 yz426 tended to have a bog right off idle. The AP squirt was a little long and sometimes mistimed. This is what the BK mod is for (drill and tap the little ear near the AP pump actuator so you can limit the actuation length), and dial in the AP pump screw. But leave this until you first get your jetting dialed.

I would probably go with a 40 pilot and one clip on the needle. Do one or the other first so you can see how it feels after.

Also, if you have trouble getting it started, I've found that the YZ426 will be a PIA to start when the jetting is wrong, but that a new plug will almost always get it fired on the 1st or 2nd kick.

Looks like you might need to run an 165main with the needle in 3rd position. For temps in the 50-90 degree range. I would leave the 162 main in and change it to the 3rd clip position first. Then see how it runs.

Post in the Jetting forum and Burn may be able to help.

Also here are some helpful tips for the YZ426 including the BK mod and others.


Get a JD jet kit....

Thanks for all the info. I'm goin wait for it to warm up before i start changing jets. Honestly the biggest problem was the way i was trying to start it. I was goin to far past TDC. Read the starting posts & starts way better. This is the 1st thumper i've owned. Last bike was 98 CR250 & i got rid of it in 99. Gotta lot of catching up to do. I appreciate the help

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