Atvs at elevation

[Npike4040]

I've taken my Polaris sportsman 400 out west the last two years and I still can't get it to have full power. First year I followed Polaris's recommended jets for the correct elevation, and it would still barely run. Ended up having to remove air filter so I could at least use it. Last year, I adjusted jet size and still had same issue. What is everyone else doing to their carburetor to get it to run correctly out west. I'm running from 7k-12k elevation.

 

[The_Jim]

I have an old Suzuki Vinson that I've never done anything with. Its been up Mt. Antero a few times, just backfires a bunch at 11k and up. Leave it stock and see what happens.

 

[Bluefish]

Rejetting is a must. Then just live with the power loss. You lose 25% at 6500 and 50% at 11k. I have a jet chart for my bikes and it’s pretty good. Usually it’s 1-2 needles leaner, 1 pilot leaner, and 3-4 mains. Now I am dealing with 45 hp to start, so it’s down to say 20-22 at 11k. Only places I had issues was really steep and above treeline.

If you removed the air filter and it ran better, it probably wasn’t lean enough. Could have also had a dirty filter.

 

[BigMiss]

I'm no small engine guru, and don't have experience specific to your ATV, but possibly relevant experience with mountain sleds. Back in the day when my dad ran his modded Yamaha triples at 10k feet, he ran 62.5 pilots when the sea level spec was 55 pilots. Seems counterintuitive, but by leaning out the mains and richening up the pilots, you're able to give better midrange performance before the main jet takes over. Between tweaking your pilots, needle height, and fuel screw, you should be able to get it running correctly. If I were starting to diagnose your problem from scratch, I would follow the recommended jet size for the mains at altitude, leave the pilots where they are at for the sea level, and lower the needles one to two steps and see where you're at. I am not sure what your engine experience is, but you could also research lean bog vs rich bog if you are not familiar.

 

[gbflyer]

Did you do the work yourself? I ask because I have taken atvs to dealerships in the past, paid for jet changes, and they have done nothing.

 

[ctafoya]

Rejetting is a must. Then just live with the power loss. You lose 25% at 6500 and 50% at 11k. I have a jet chart for my bikes and it’s pretty good. Usually it’s 1-2 needles leaner, 1 pilot leaner, and 3-4 mains. Now I am dealing with 45 hp to start, so it’s down to say 20-22 at 11k. Only places I had issues was really steep and above treeline.

If you removed the air filter and it ran better, it probably wasn’t lean enough. Could have also had a dirty filter.

This.

 

[D_Dubya]

How old is your machine? It’s not an old 2 stroke is it?

 

[LFC911]

That's why I bought something with an efi.