I think for every 2500 feet you change in altitude, you need to change 1 jet size. I would probably go with 2 sizes smaller than stock for where you live and ride. Then, I wouldn't worry about changing it again unless you went down to sea level. It may be a little rich at 10,000 ft., but that's ok.

 

i live at 4500ft, and ride mostly around this altitude and have dropped 1 size (5 points i believe it was) and it really helped. But, i recently did a run to 7500ft, and it started spitting/sputtering pretty bad, and had to use low for anything but flat ground. if you are going to 10,000, i would go at least 2, and maybe 3 down, but would want to change back when coming back down. remember too, you loose approx. 3% per 1000ft altitude in horsepower, so that is 30% less power at that altitude.

 

If I remember correctly when I went to flagstaff from phoenix I would run a 122main jet in my prowler.The cinders at flagstaff are about 7000ft, stock jet was like a 138 I think. I will tell ya that the # of jets sizes I dropped was huge but it ran good.

 

Thanks all for the suggestions. I dropped from a 132 to a 130 and it ran perfectly at altitude. Also, the plug looks good after being use at its base altitude.

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