What jetting for altitude of 9-12,000 ft?

[JD1515]

I currently have my 400 jetted with a 170 main jet. It has a full exhaust and k&n intake with no lid. I live in missouri and probably never ride over 1000 ft. So if I go to colorado in the next few weeks and will be between 9-12,000 ft elevation, does anyone have recommendations on which jetting. I don't need it to be perfect because I was able to run last summer jetted the way I was but it obviously wasn't jetted that great. I was still able to ride though. Is their a rule of thumb for example that says for every thousand feet the jet should go up one size? Can someone whos ridden in that altitude give me some help?

Thanks, Joe

[exrider12]

I think you lean out your jetting. Id try go leaner two main jet sizes,and go leaner on your needle. Some one might be able to help you better.

[JD1515]

I know I need to lean it out, I just dont know how much. I am going to buy 2-3 main jets that I can take with me while I am in Colorado but I would like to keep from buying a bunch of them.