I'm absolutely amazed your ATVs ran at 12000' if they're jetted for sea level. I used to have a Rincon and since I lived in Reno, it was jetted for 4000-6000'. I once took it up to 10k and it ran so badly I had to remove the airbox lid to get more air into it just so it'd run well enough to make it down into thicker air.
Likewise, my Grizzly 660.. it was jetted also for 4000-6000, and we were riding up above 8000' last Summer and it got to where it simply wouldn't climb anymore because it was jetted too rich. Once I dropped it down from a couple of jet sizes, it ran great up there.
I'm going to buy an altitude compensator for the Grizzly eventually, but they're about $230 so I haven't been ready to spend the money just yet. Fortunately, my Sportsman is EFI so I don't have to worry about it.
Rob
I ride my Honda Ranchers around 8-10,000 feet without any problems and they aren't jetted.
Traveling Whitehouse
2006 Keystone Raptor 3612DS
2004 Chevrolet Silverado 3500 CC LB DRW Duramax LLY 4x4
Reese 20K Hitch
Prodigy Brake Control
2007 Honda Rincon & 2000 Honda Rancher
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