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high altitude riding

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what all is involved in prepping the carb to run in the high altitude.....is it just a tune up or a rejet.

im planning on doing alot of riding and wanted to keep my '04 stock so i didnt run into naggy carb problems when im out in the middle of nowhere.

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on a 4-stroke, i wouldn't do much of anything until around 10k feet. then i might go 1 step leaner on the main jet and needle. or i might not. low-performance thumpers like the xr's and my klx don't seem all that sensitive to altitude. my bike runs great from sea level to 10000' or so. then it's slightly more stall-prone cuz it gets richer, but it's still perfectly rideable.

mw

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Hate to disagree with you Mark but my XR ran like S#$t at 8400 feet with my current jetting. It was really fat on the bottom end and ran OK mid-range and above and I had the fuel screw all but 1/8 of a turn out. I had to go down 3 sizes on the pilot jet and drop the needle one notch to get it to run right. I live at 2500' and ride to about 4000'.

What kind of elevation are you at now and what is your current jetting? How does the bike run? Finally how high are we talking about?? 7000, 8000??

Give us some more details.

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For this response, I assume you're talking about an XR400. Regardless, you'll get best performance with a rejet, although it's not necessary if you're willing to put up with subpar performance, throttle response, mileage, cranking, plug life, etc. High altitude jetting has been covered pretty well here. Most recently, I had this discussion.

If you plan to keep the bike entirely stock, use the sea-level "Trail Riding" settings (60/158) compensated for altitude using the accompanying charts. At my 5,300 ft altitude, the compensation factors are roughly 0.89/0.95 (slow jet/main jet) so the "Trail Riding" jetting would be 52/150. Change jets, then fine tune the idle air mixture screw for best idle, and have fun :thumbsup:.

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