I had my carb jetted for 5000-8000 feet because that is where I will spend the majority of my time. In Billings, MT where I actually live Im at about 3700. Any ideas on what this will do to my engine? I mean, it runs fine, but will it run a bit rich, or lean, or what? Anything I can do to compensate for this, or should I not even worry about it?

 

If you get a jet kit there will be as many as 10 jets in it to play with. A dial-a-jet gives you the ability to turn a screw and change you jetting. They don't list the 400 but it takes the same kit as a 500. Do a search for dial-a-jet.

 

Its gonna be leaner at lower altitudes. The air is thinner at altitude so, less gas is needed. The main jet is most likely one or two sizes down, from stock.
Be aware of drivability symptoms of running lean, so you dont cause engine damage.
Some people use vents in the air box lid, and jet for lower elevations, then when they go up in altitude, they open the vents up, to lean things out. Its safer than, jetting for high altitude, and then running at low altitude.
Hes an article showing the symptoms of lean,and some of the things you can do to counter them.
http://www.motorcyclecruiser.com/tech/jetkit/

 

It engine needs to be richer the lower you go, not leaner. You lean it out for higher elevations.

 

Thats what bkcntyxplr asked, "Will it be running richer, leaner, or what? Hondabuster stated "It will be running leaner". With his presesnt jets, his ATV will be running leaner at the lower altitude.

 

Read it backwards I guess. Sorry, guys.

 

No problem. Just didn't want the guy confused.

 

Thanks for the info fellas. I'll have to talk ot the dealer to see exactly what he did, and what my options are.

 

Stock sealevel jets should be fine at you elevation. Mine seems to funtion ok until about 5,000 feet, then only the idle needs to be leaned out. The dial-a-jet system is a way to put an adjustable jet in your carb without the jet needing a needle to adjust the fuel flow and still be adjustable. The dial-a-jet lets you lean it out with an adjustment screw (or 2) mounted on top of the carb. It bleeds extra air into the system to lean or less air to enrich the system for altitude adjustment or if you run 2 different exhaust systems or sometimes you run with the air box cover off then sometimes with it on. Very flexable system, but you need to learn what adjustments to make and when by playing with the system. Their literature is very good and the system has been around a very long time.