Hot Jetting Setup for NC/SC area? (450F & 250F)

Guys (and any gals),

Just moved from San Antonio, Tx (800 ft) to the Asheville, NC (2400 ft?)area. Having troubles with the bikes running too rich...I think. We've got an '04 YZ450F and YZ250F...stock 'cept for air filter cage screen removed. Jetting was perfect in Texas. Now, neither will idle with the choke off. Choke dies. This is kind of strange, because I thought the bikes were running too rich at altitude with reduced air density. So, I'm not totally clear what function the choke on these YZFs is actually performing. Is it adding more fuel, or cutting down the air flow, or cutting down the fuel flow? The manual leaves everything to the imagination....or I haven't found the right page. Bikes backfire out of the exhaust, so I'm assuming rich misfire.

I cleaned the carbs, adjusted fuel screw, lowered needle, adjusted accel pump, but no go. Originally we thought the symptom was reserved for the 250F, but it showed up on the 450F today too (after a 2 hr drive to a track...what fun). The bikes will run at high (high) idle, but piss and moan with an exhaust flame to boot....too rich. They symptom also showed up on the '04 and '05 DRZ110s we have. The '04 DRZ 110 has an opened up air box and pipe, ran ok with little "tuning". The point is, jetttins is way off on all the bikes. I suspect they're all too rich because of altitude.

So, what's the NC and SC riders are using for '04 250F and 450F? I'd appreciate any help you can provide.



Needle & Pos:


Out of curiosity, are the bikes jetted for specific regions prior to arriving at the dealer US?


Hey Jack and welcome to Asheville. If you don't get your questions answered here, go see Zeke at Harper Yamaha in Hendersonville. He's the best YZ carburator guuru around. I was having similar problems with my 426 because the areas I ride around here have 1500 to 2500 ft elevation differences, problems no more. Good luck! :applause:

can't help you with the 250 but my 05 yz450 pitched me some fits before i figured it out. i run the powerbomb header with the powercore4 along with the rear powernow. i ended up way leaner than i ever thought,40pj,100paj,DWR(04wr450)which is a leaner needle-3rd clip,160mj,stock starter? any richer than that and it would spit,skip,and occasionally die. i ride from 1500-5000' and this is whats working in the heat :applause:

Thanks for the suggestions guys. You've recommended changes in the direction I thought I needed to go. I'll call Zeke too.


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