My 400ex which has about 15 hours on it runs fine and idles good.I noticed yesterday after starting it up in the shop to let it run for a few minutes the headers were glowing,It may have done it since I've had it but the shop lights were off and it was the first time I saw it do that.I called my dealer seeing it's under warranty and explained it to him.He stated the stainless pipes were thin and it was common for them to glow and said not to be concerned.I may be wrong but I feel like it is leaning out but I do not want to tamper with the jetting due to the warranty.Any tips?

 

There are dozens of ATVs from all the OEMs on the market that do this and it is normal when the machine is not being ridden to help cool it down. A 400EX is one of more prone ones to do this....especially in stock form with stock jetting.

Most people never realize that they do this unless out in the woods parked along side the trail at night. It's nothing to worry about so long as you aren't letting it idle for extended periods of time when already at operating temperature. Doing that will decrease the life of your exhaust valves significantly on any air cooled engine.

 

Yeah, like knowsalot said, it's and air cooled engine and will get hot when sitting still, idling. Very typical for the header to start glowing.
Honda also sets their quads to run on the lean side to pass the California emissions standards.

 

Yeah I found the same thing on my 04' 400ex that I purchased used and and thought that the guy I bought it from pulled one over on me untill I searched it here and found that in most cases it is considered normal. Not to hijack your thread but if I upgrade the exhaust header will this stop?

 

Thanks guys, Fowler actually any modifications in my opinion will make it worse such as aftermarket header/exhaust, K&N ect causing a more lean condition or not enough fuel.I think the only correct way to improve it is to rejet the carburetor or try to richen the idle mixture screw out a bit "mine has that darn D shaped head" and tune it by the plug readings.If mine did not have a warranty I'd be correcting the issue.