Recently, I washed my 2003 400EX and decided to start the machine to dry off the engine. While holding the throttle about 1/3 of the way open for about two minutes, I noticed that my pipe coming out of the head was begining to glow more and more red. After letting the engine return to idle, the red glow immediately began to go away. Keep in mind, it was almost dark outside when I was warming up the engine. I became concerned that my carb may be running extremely lean, and went to talk to the local Honda dealer in hopes of preventing any further engine damage since the ATV has less than 40 hrs since it was bought. The dealer told me that this glowing was normal when the pipe is viewed in the dark or dim conditions since the pipe is only one layer thick, as opposed to two layer pipes in the past. He went on to say that if you took any stock 400EX down the road at night it would look like a light show because of the glowing pipe. Can anyone with a stock pipe tell me if your pipe glows in the dark or can someone start their 400ex in the dark to see if your pipe also glows? I have never seen the pipe glow in the day, only when its dark, or in a dimmly lit area. Thanks for your input.

 

I am by no means an expert but my guess is that your engine was getting pretty hot. It is an air cooled engine and you were giving it throttle for 2 minutes without moving. No air flowing over engine equals higher operating temp. I bet your carb jetting is fine. BTW, buy a wash plug to prevent water entering the exhaust. Helps a lot when washing!

 

BS

i know that's BS

sure, sitting for a few minutes with throttle open is one thing, but going down the road glowing? NO, i've done enough night riding to know that that isn't normal. i've rejetted mine for the mods i've done, but have also ridden with stock bikes that do not glow.

have you done anything to your honda?

 

No mods, its 100% stock, nor have I ever made any changes to the carb screws.

 

try doing a plug chop just to be safe. maybe yours came lean like that... our didn't.