Need some Turner Help!!

Hello all,

I need some help with my 2003 WR450. I have a race this weekend, and my bike won’t idle.

Story: Last week during a harescramble race, I stalled the bike going over a small log (about 4” round) and ever since then, my bike will not idle properly. Once started, the bike will only idle for 5-10 seconds before it dies and the throttle has become extremely touchy right off idle.

Since the race, I have cleaned my air filter, and my carburetor. I thoroughly cleaned the carburetor with carb cleaner; I removed all of the jets and sprayed carb cleaner through the jets, and the passage ways that the jets are seated in. None of this seemed to help.

Other symptoms: The bike won’t start unless I choke it, no matter what the temp is. Usually I can get the bike moving if I leave the choke out until the rpms are up. Then I shut the choke off. Once its past idle, the bike runs decent through out the rpm range, but I am noticing a little bit of “poping” or slight backfiring that wasn’t there before. After 2-3 minutes of riding, the bike will stall and die if I let the rpms drop to near idle. Blipping the throttle or turning up the idle adjustment screw doesn’t help.

Please Help??? Where do I start looking??? Bad gas?? Accelerator pump??

FYI, my jetting is only slightly richer then stock. The main is 158 vs 155 and the pilot jet is a 48 vs a 45. This set up has worked great for the last 7 races.

Put in a new spark plug, prob'ly gas-fouled it....and only use NGK plugs, that's what works best! :cry:

Any chance your carbs vent lines got smashed closed? Or pushed somewhere they are getting pinched?

plugged pilot jet,air leak,stuck hot start.......just some ideas.

Check valve clearance and put in a new plug. Still bad?

If the engine backfired when you stalled it you could have blown the carb off. Check the carb boot between the head and the carb. OK? Take the slide out of the carb. Is the roller slide OK? Check the floating plate in front of the roller slide. Broken, cracked? Replace if bad. (the center notch goes down) Check the seal between the roller slide and the plate. Very important that the seal is good.

Good luck finding the problem.

Hey guys.

Thanks for the help and ideas so far, but unfortunatly, I’m still having a problem with my bike. Since I first posted this, I have thoroughly cleaned my carburetor and air box. And by “thoroughly”, I mean I removed my sub-frame and air box from the bike and disassembled it completely, every part was meticulously cleaned. I did the same with my carburetor as well, every jet was removed, inspected and cleaned, every diaphragm, slide, and spring was inspected and cleaned as well. Everything was scrubbed spotless with a toothbrush so I can confidently say that DIRT is definitely not the cause of my problem.

Besides cleaning everything really well, I checked my valve clearances, they were good, I have also put in a new spark plug, and returned all of my jetting back to stock settings. 150 main vs 158. 45 pj vs. 48. Needle in 4th position verse 5th and 1.5 turns on the pilot screw vs 3 turns.

Unfortunately, my bike still will not idle. It will start very well when it’s cold, and idle for about 10 – 15 seconds before it starts to act up. If I turn my idle control way up, that will help a little bit, but once the bike get warm, it won’t idle at all. It seems to me like it is running rich. I say this because, I can get the bike to run if it is cold, and I just started it up. However, in about 4 – 5 minutes the bike will eventually stall at low rpms. Once it does this, I can’t get the bike to start again unless I let it sit for about 20 – 30 minutes. Then it fires up on the first or second kick.

Any other ideas out there??? :cry: I’m stuck.


Have you tried checking your electronics, CDI, pickup and coil??? It almost sounds electrical in nature.... Runs till its warm then it goes to crap. I had a bad primary one time that did the same thing

Hello all,

Just wanted to give an update so we can all learn from my misfortunes. This problem turned out to be a loose cyclinder head bolt.

Wow :p it was that loose that it created a vacuum leak? :) Good to know! :)

Yep it was pretty loose. About finger tight. The other 3 bolts were good and tight. I'm lucky I didn't warp my head from metal expanding and contracting during operation.

The worst part is that it was one of the bolts that is visible from outside the motor. I'm still kicking myself over that.

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