I am going to colorado for 2 weeks and just want to know if my 650prairie and 400eiger will do in mountains? I really dont want to rejet for 2 weeks of site seeing.

 

service manual calls out 0-1600 ft front 138/142
1600-4900 ft 135/140
4900-8200 ft 132/138

so depending on the elevation you are going to, you may need it, or you may just be able to pick up a freeer flowing filter to lean it out.. local folks would know better..I'm at sea level..
if I were taking my street bike out there, I'd drop down a jet size..

 

Rejet. Trust me. When I moved from Sea Level to only 6000 ft My machines ran so bad it was unbelievable. You'll kick yourself if you don't rejet - it's just a fact of life in the mountains.

 

I belive that...
6000' sounds like about 2 jet sizes...smaller,
I bet it ran like crud, being that rich...
there used to be a place that would give you the elevation
of any town.. a help for folks taking their toys on vacation..

 

I live at about 400 ft and ride anywhere from sea level to 8,000 ft. I've found that my Bomb rides just fine up to 6,000. It does loose some power, but still has enough umph to get up the clibms. Higher than that and it starts to bog. Where altitude is really telling is when you are over 9,000 with a cold machine. It can be pretty hard to get your quad started on cold mornings when you're up this high. Just be glad you're riding a thumper. Two strokes foul plugs like crazy in the high country.

 

For a two week trip I wouldn't bother rejetting. I would however do something to the 650 to open up the intake, shop vac hose or the new intake from DiamondG racing. That should be all you need for altitude. Put the original back on when you get back home.
My Eiger seems to do fine here. With a clean and not over oiled air filter it is actually jetted almost perfect. Plug reads for what they're worth indicate both quads are running fine. Light sandy brown color. I've done nothing to the Eiger and only modified the intake on the Prairie.
I live at 6400 feet and my riding takes me up to 8000 regularly. Since we have this huge fire in the San Jaun Forest it doesn't look like I am gonna get to see how they run at 10-12K this summer.

 

See my comments on venting your airbox in the "Other ATV Topics" section. This is such an elegant solution to the need for a QUICK BUT TEMPORARY REJET!!!!