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Temporary high altitude jetting

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How much performance degradation occurs going between 8000 feet and 11000 or 12000 feet? For going over a high altitude pass in CO, should I plan to rejet my XR650R for just the crossing? (And is the answer different for my CRF250X?)

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My XR is jetted for my house altitude, 5700 feet. It runs fine from there to 12k. All the trails I ride are in the San Juans so that goes from 8k to 12k all day long.

You may need to turn up your idle speed higher above 10k but everthing else will be fine I'm sure.

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Qadsan posted the numbers before but I forget. I think it was 3% power loss for every 1,000 feet you go up. Don't quote me on that.

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How much performance degradation occurs going between 8000 feet and 11000 or 12000 feet? For going over a high altitude pass in CO, should I plan to rejet my XR650R for just the crossing? (And is the answer different for my CRF250X?)

There's roughly a 3% loss in power for every 1,000 feet in altutude above sea level. Another tidbit I had in my notes was for every 10°F of heat above the standard 59o F, there is a 1% loss in power loss, which is part of this 3% and not in addition to it. These are not hard figures by anymeans, but if you know the specifics of the air temperature, barometric pressure and relative humidity for your riding environment, I can calculate an apprxomiate loss in horsepower as well as correction factors.

As far as jetting suggestions, here some info I put together for Eric pigpen site as place to start for the XR650R www.xr650r.us/jetting

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