My 400ex is running rough, won't stay running

[wheelman]

Guys,

Just bought a 1999 400ex and looking for some guidance. Overall she seems in good shape, but I've now noticed that it doesn't seem to want to stay running at idle, even when its warm. At first it wouldnt start but after learning the two quick throttle pump trick before starting, I can get her fired up quickly most of the time. After that however, it sputters and wont run smoothly at idle and dies. It seems to run okay when I keep it moving.

I've posted a video to show you the problem I'm having.

400ex wont stay running (http://www.youtube.com/watch?v=_JZ4jyHOwzQ)

The air filter & box are squeaky clean, and the plug was slightly dry carbon fouled, but nothing that looked serious.

Any ideas on where I should start looking?

Thanks,

Brandon

[BenHonda400ex]

Is your gas gauge turned off? Because I that's the only answer I have.. I meean mine doe's that little gasp for air like one or twice when I first start it up then it stops...

[CJM]

Does it idle good once it warms up or does it keep stalling till you are moving?

All 400ex's are cold blooded, when cold its a pain to get them going and then keep them going for a bit. Could change out to a 40 pilot and see if that helps or adjust your air to fuel screw maybe a half a turn.

[wheelman]

Here's a couple of pics of the plug.

https://lh4.googleusercontent.com/_TjWmsQ4uLMo/TVHgSeotEYI/AAAAAAAABGo/TWvgfdLUiOY/s800/2011-02-08_16-44-31_476.jpg
https://lh3.googleusercontent.com/_TjWmsQ4uLMo/TVHgP81mTXI/AAAAAAAABGg/b_GYjebYoVw/s800/2011-02-08_16-44-46_185.jpg

[wheelman]

Originally posted by BenHonda400ex
Is your gas gauge turned off? Because I that's the only answer I have.. I meean mine doe's that little gasp for air like one or twice when I first start it up then it stops...
Gas was set to on. It run for a good 5-10 minutes before I took the video, so it should have been completely warm but it was still dying.

[MidnightBlade]

get a new plug, mine did the same thing, plug looked the same as yours (minus all the rust and mud and stuff) put in new plug and it ran perfect. i would also bump the pilot up to a 42 works wonders on these ol girls.
then, if that dont work clean the carb good and adjust the valves

[MO-EX-RIDER]

mine does the same thing when its cold, once warm it goes away, it goes away with a 40 pilot and the right setting on the a/f screw