If I have an ATV with carburetor bought and used at 500' elevation, how will it run at 8000' elevation? Do I need to rejet or will it run well enough for a hunting trip?

I have an old Honda. Going from 750 feet to 9,500 has never been a problem except to bump the idle up a bit.

I used to have a Honda trail bike with a switch for high elevation. Does anyone still put those on?

There's a thing called Dial-a-jet. You rejet the carb too lean and then use that to add fuel in increasing amounts as needed to get back right. I have zero experience with this stuff. So I can't say if it works or not.

Due to lower oxygen content in higher elevation air, you will lose about 3% of engine horsepower per 1000 feet of climb, IF your carb is rejetted leaner to match the elevation. So if gain 7000 feet, would loss about 21% of rated horsepower. If not rejetted, you will lose more than that as the fuel/air mixture will be too rich, may see some black soot in the exhaust pipe. Your dealer may have chart for which smaller carb jets to use at various higher altitudes. If you rejet for the higher altitude, you must immediately reinstall your low altitude jets when you return home, or you will damage the engine with a too lean mixture causing overheating and pinging.

I have taken two carburated Yamaha 350 ATV's that were jetted for 4000 feet up to 6000' to 9000' for a 10 day hunt. Other than the expected power loss, they ran OK.

Later bought a Yamaha 550 Grizzly with EFI, great machine, it automatically compensated for the higher altitude, lower oxygen content air.

We live at about 4000'. I've had my Razor up to about 9k with no noticable change in performance. Apparently the EFI takes care of the fuel mix automatically.

The OP wants to go from 500 to 8000 with a carburated atv. That will likely see a significant drop in performance if not rejetted.

rejetting isn't that tough.....do some research or just pull the jet see what # it is...

get a leaner one for 8K'

lots of info out there......EFI on newer machines is great !

https://www.polarisatvforums.com/threads/re-jetting-for-high-altitude.6709/

Check with your dealer, you may need more than a jet change, like needle clip and adjustments. The lower powered CVT ATVs can involve weight changes for high altitude.

^^^oh look! Rick has a sock puppet!

You should also take a good tire pressure gauge for low pressure ATV tires. You’ll gain about 0.5psi per 1,000ft of elevation gain. You’ll drop about 1psi per 10*F of temperature drop.

Not about carburetor jetting, but just as an aside, that altitude really reduces engine horsepower too and I never gave tire pressure a thought, but that makes sense too. It was pretty funny what that Colorado altitude did to my fun size Snickers bars. We hunted up to 11,000 feet and my Wisconsin Snickers bars were like little pillows full of extra air. Real thin air for this flatlander though use to 500’ above sea level.