I have a 2001 honda 400ex. It does not like to idle because it cuts out and dies. It runs ok most of the time when I am on the throttle, but occassionally it cuts out and misses several times. It automattically backfires anytime I let off the throttle when I am riding.
I first thought it was the coil, so my friend has a 400ex, we swapped the coil, no change. We swapped the rev box, no change. I had an extra stator, swapped it, no change. I changed the oil cause I had gas in the oil, my header pipe glows when it idles. Any ideas?

 

dirty carb, jetting, dirty air filter

 

Check your intake rubber make sure there are no cracks or separated spots between the
carb and the head. If it sucks air in it will make it backfire and run a little different.

 

Ditto what these guys said. It sounds like it is running lean. I'd suspect partly gummed up idle circuit, and also check for intake leak.

 

I will check for leaks first, then jump into the carb and see if anything is dirty. I am not able to adjust the idle, no matter what I do it does not make any difference. I will update with a response as soon as I complete the tasks.

 

sounds like a dirty carb more then a air leak

 

Try changing the plug, I had an 01 400 as well and I noticed that a lot of them foul a plug really easy and they tend to do weird things sometimes.

 

Just wondered if you found the problem with your 400ex?. I too have the same problem and the carb looks very clean inside.

Jeff