99WR400 pops/fouls plug

I recently posted similiar post about the jetting. The jetting is std except for a 172MJ, settings:#3 on needle,FS at 1.25 may try 1 turn.The problem is at low to mid throttle. I haven't rode the bike that much, at first it was rare to foul a plug or pop/miss and almost foul. This usually happened at a race. I thought maybe washing the bike and it setting for a week and re-firing it was water/moisture. Then in the winter the problem got even worse which then I thought maybe it was too rich. However recently it seems to happen every ride(at first crank only) but now its at first and during a ride even with it warm. I tend to think maybe coil and or moisture or rust on the stator/pickup. The reason is that I "heard" the bike was sunk and had water sucked up and had a new engine replacement(rebuilt/ replaced I don't know)I've decided to check and clean cdi,stator, TPS etc.. just in case of rust.If no rust or heavy moisture restricting the fire I'm stuck again. Has anyone else had a problem with ignition with similar problems such as the pop/miss and fouling not due to jetting?Any other suggestions that I may miss while troubleshooting this?Thanks

You need to give us more info on the jetting. What pilot jet, starter jet, needle, and pilot and main air jets does it have?

My '99 had started fouling plugs left and right last summer. (The cam timing on my bike is set to YZ specs so it wants to be leaner than stock anyway, but what I'm saying may give you some idea as to what direction to go.) Before that, I had the plug that originally came with the bike. It seems that the jetting just wasn't lean enough. I am running a 35 pilot jet and the pilot air screw is set equal to a 45 paj. (BTW, I'm usually at sea level.) Leaning the pilot circuit by going from a 65 to a 45 pilot air screw really helped both the plug fouling and made the bottom end much snappier. I'm runnning the stock muffler with a homemade buttplug, er..baffle.

Some other things to check:

The spark plug cap had gone bad in '00 and I had to replace it. The bike fouled plugs intermittently. Those damn caps are expensive! Get a little Motion Pro spark tester to make sure the cap is still good. Also, check that it is attached firmly to the high-tension wire. It screws on to the wire and can come loose. One thing that really helped a lot was unplugging the sky blue wire. (It supposedly weakens the spark at idle for noise emissions control when it's connected.) Just pull it out, tape over it and it will definitely starter easier.

Although it is not likely part of your problem, the accelerator pump diaphragm and rod are very susceptible to corrosion. The water gets into the AP via the little rubber accordian boot on the actuation rod. You need to seal this up w/ silicone.

Also there is MUCH to improve on your stock jetting and your accelerator pump operation.

Thanks, I have unplugged the gray wire and taped. also plugged the ACV. It will be this fri or sat. before I tare it down, I'll have much more info then. I also remove and clean the accel pump pretty regular. The first time it ran great, a couple of months ago when it started popping again I cleaned it again but no change, its been progressively worse since. Everything was put back correctly. I think its something else. The reason I'm tending to rule out jetting is due to the fact that it keeps getting worse regaurdless of temp, gas, plug etc..I'm thinking jetting would tend to fluctuate the problem along with temperature, but it seems to be worse with time instead of temp change. I live in Alabama so one day it may be 60 and the next 35. Atleast this has been my observation so far.

That's why I suggested an electrical problem such as the spark plug cap. Also, the gray wire and blue wire are entirely different. Gray wire affects low-mid throttle, blue wire affects starting.

is it an intermitent(sorry cant spell) problem? do you have the hot start button on your bike? it sounds like my bike did when mine was leaking air in, couldnt work it out for a couple of weeks but that sorted the problem. does it idle ok?



Rich in Orlando:

Where is the sky blue wire?


yes, it idles fine once it warms up and even during warm up with choke on(choking 30seconds or so).However, it will not idle when the miss/ pop starts. It is intermitent, but seems to be pretty regular now. Last 3 rides every time. But once I run the $hit out it the problem goes away until I stop for a while and it re-occurs out of the blue. It has an aftermarket hot start that runs to the handle bars. I think they called it a Hawkins hot start, seems like I remember seeing Motion Pro on the tube. Your right though, During a race I endoed, got back on and fired it up and began riding, ran like crap, evidently my leg or boot flipped the hot start on, I stopped but no idle, when I took my helmet off and cranked again I heard the air sucking in thats the only way I figured out what was wrong. I remember now that the pop/miss its doing now sounds exactly like it did that time. The problem is I wonder why it idles so good?? Good catch, I'll look that over as well. Thanks

I appologize. The sky blue is the one unplugged. The gray wire is located? I found the grey wire pics, one pic shows a 2 wire black connector another shows a 6 wire clear/white connector. One pic was a 250F, just different connectors?Thanks

It's the solid gray wire in the 2 wire black connector.

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