I have two 2003 400ex's both of them are stock except for a slip-on pipe on one. I have one that is running great and one that is being a pain in my rear. The one with the problems starts fine, idols fine and runs fine for a little while. However it doesn't last long after that. I first thought it was a dirty plug so I put in a new one with no luck. So then I thought it was a dirty carb and not having the time to work on it I dropped it off at a local shop to have them clean it and check it out. They told me my rectifier was bad and my stator failed one of three test. I didn't want to pay the crazy amount they wanted so I brought it home and ordered the new parts from Ricky Stator. I put in the new stator and rectifier and it still has the problem. So being that I have it's twin sitting next to me I swap the ICM first with no luck and then the coil. After all that it is still running like junk. The problem itself feels like it is either cutting out or loading up with fuel and the bike jerks back and forth. If yall having any ideas please let me know. Thanks

 

You don't say if the shop actually cleaned the carb. If they didn't, this could still be your problem. I would swap carbs and see if that cures it.

 

Unfortunately I can't say for sure if they did now. They said they did but it doesn't seem that way. I knew I should have just went somewhere else when I saw the old mechanic wasn't there. I'll try swapping the carbs this weekend. Thanks for the help.

 

Does the one that runs like crap have the slip on? If so, was it re jetted when the pipe went on?

 

Try berryman carb deep cleaner, works all the time.

 

The one with the problem does not have the slip on pipe.

 

Swapping carbs might not work if the other is jetted for the pipe. Pull the carb and clean it.

 

That does sound like an electrical problem, starting and running fine at first when it is cold, then running poorly is usually from something in the electronics heating up and expanding, causing a circuit path to open and create an intermittent problem that can be a pain to track down. You have replaced major components, and it still runs poorly when warmed up, by ICM, do you mean the CDI ? You have replaced the source of you voltage, with the Ricky Stator parts, along with the coil, that only leaves the CDI for spark control. One other thing to consider is the kill switch circuitry, any damaged wiring there could cause problems as well, try unplugging the kill switch on the handle bars to see if that helps, could be you have a damaged or failing switch grounding out your spark partially, and causing rough running.

 

It's not that it only does it when it's warm. It does it about mid throttle or so. I think it's a dirty carb I just didn't get a chance to clean it last weekend. The ICM is the ignition control module.

 

So here is an update to this problem. The bike is fixed and running great. This was not and electrical problem or a dirty carb thing. This was a bad plastic valve on the side of the carb. After I replaced the valve the quad runs great. Thinks for your suggestions on thus and maybe it will help someone in the future.