CDI unit on 99' WR400F

Hello everyone. My bike (1999 WR400F) has a major problem. It barely runs. When it finally starts it will die again at idle. It crackles, sputters, backfires, has no power, and the plug is fouled with black, dried carbon. I think it may be an ignition problem so I checked the ignition and stator coils and the throttle position sensor and they all seem to be ok. So my question is how do I test the CDI unit? If you know how to test it or have any other ideas of what may be wrong your help would be appreciated.


any mods to your carb?

When is the last time you COMPLETELY disassembled your carb for an unbelievable cleaning?

Kevin’s right, disassemble the carb, use a can of carb cleaner and compressed air.

Where goggles, carb cleaner is murder on the eyes! :)

When was the last time valve clearances were checked? Hard starting is a symptom of valve clearance being too tight. If the bike has been run like this for any length of time you could have burned valve seats.

I bought the bike a little over a year ago used from a dealer and it has ran absolutely perfect up until now. I regularly change the oil and clean the air filter but I haven't taken the carb apart yet so I'm not sure if any mods have been made. I know a guy who has a DRZ and my WR is remarkably faster so I'm guessing there has been some mods done. I'm going to clean my carb out today and if anyone has any suggestions on what mods to look for or to performe that would be great. I'm very new at this and all of the help that everyone has given me is making my learning experience that much easier.

I haven't checked the valve clearences yet but it sounds like I probably should.

Thanks again!

I doubt your CDI is bad. I wouldn't be at all surprised if you have a loose spark plug cap. The cap and the high-tension wire are not permanently connected. They can and do come loose. It's bitten me in the butt more than once, the most recent was just a few weeks ago. I had just done a valve adjustment and was on the first ride since doing the work. When I test rode it around my neighborhood it ran fine. Once I got into the woods a few days later, it ran just like you described. I did a complete disassembly and cleaning of the carb (luckily I had a fresh can of carb cleaner in my toolbox), messed with the jetting, and it still ran like crap. As a last resort, I took off the spark plug cap to test the spark and I found it very loose. So, I screwed the cap back on the wire as tight as I could get it (the cap has a screw that bites into the end of the high-tension wire), put it all back together and it ran like it was supposed to.

I missed a half a day of riding a couple of years ago just because of a loose spark plug cap. That is going to be the FIRST thing I check from now on if the bike's not running right.

CDI failure usually is complete and results in a non-runner.

Partial failure is rare in my experience.

Gut your carb. Remove the air horn on the airbox end of your carb as well.

If you have not checked recently, the accelerator pump on the 98/99 is NOTORIOUS for getting crapped up and seizing. Water goes down the accordian boot that seals up the AP actuation rod. I silicone mine on both ends now.

When you take apart your AP, BE SURE you get BOTH O-rings re-installed! One is famous for falling out. You will develope an air leak w/ that missing.

Use carb cleaner AND compressed air to THOROUGHLY blast the air ports that reside under the air horn. This would be your pilot air jet and main air jet. These can, and will, plug up from a freshly oiled (over oiled?) air filter.

Check your float height. These models were also sensitive to float level. Thoroughly clean all jets/ports on the rest of the carb as well.

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