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Colorado Jetting

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Hey guys. I have a 2006 yz250f with stock jets. I am originally from the midwest and the bike ran great with a few minor mixture adjustments here and there but I have moved to Colorado and I live at about 10,200 ft above sea level and I know I am gonna have to rejet my carb. I know none of you can tell me the exact sizes to go with but does anyone have a "general" idea about what size I should be looking at. I was personally looking at 1 or 2 sizes smaller of JD jets, but any advice would be greatly appreciated. Thanks guys

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10,200 is high. Where are you in CO? Not familiar with the carb on your bike But I wouldn't go more than one size smaller at a time. A clean airfilter is critical. Suggest ADV Rocky Mtn forum for local guidance.

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Here is a direct answer to your question.

Your bike came with a 175 main, 48 pilot.

Leave the pilot at a 48. The thin air can't pull as much fuel through it as thicker sea level air can.

 

One main jet size for every 2000 feet. So...

175 SL

172 2000 feet

170 4000 feet

168 6000 feet

165 8000 feet

162 10000 feet.

 

I would start with a 165 and see how it runs. Don't confuse slower throttle response and less power with poor jetting. You may be exactly at 13-1 Air/fuel ratio, but the higher altitude still robs a lot of power.

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