WR450 won't idle

2005 WR450F, purchased used last year. Pretty much stock except for a PMB exhaust insert, red anodized fuel mixture screw (zipty?), and AIS removed. Ran ok for a year at 200-5000 ft altitude but seemed to need the fuel screw backed out too far, 3-4 turns at sea level. No pop on deceleration. This week I pulled the float bowl to check the jets and found a 168 main and a 48 pilot. Also found the clamp between the carb and the cylinder was loose. Put it back together and it seemed to run great up the hill for 1 mile and then died. Now will not start or idle, hot or cold, without the choke. Will hold mid and high rpm with the choke pushed in but runs rough and pops. I have pulled the carb off three times. Cleaned the air filter. Replaced the pilot jet one time because on the second look, it was a little clogged. The carb bowl smells a little bit like varnish but is visually clean. I replaced the aluminum mixture screw with a Scotts and a new o-ring. I either lost the original o-ring during all this disassembly or it was never there. I have hit it with a can of carb cleaner and compressed air. I concentrated on the passages between the pilot jet, the mixture screw, and into the carb. When I squirt cleaner into one place, it comes out the other two places. Any ideas what to try next?

Well all the symptoms pointed to the pilot circuit. Everybody said check the carb; my friends, TT's Burned, and finally the local shop mechanic. After the local shop mechanic looked at it, he thought it was the ignition and had to hear back from the factory. Then he found that was ok but found the small AIS fitting had fallen out of the cylinder causing a vacuum leak (right hand rear corner of the cylinder). Not the large one on the front of the cylinder near the radiator. The previous owner had pulled the 1/4" hose off and just capped the fitting. Well, according to the mechanic, the fitting had fallen out:excuseme: He tapped it and put a sealing bolt in it. Seems to have fixed the problem.:thumbsup:

The good news, I got pretty good at pulling the carburetor off the bike and now understand the fuel circuits better.:devil:

good to see the problem and solution - i guess that's another thing that we should keep in mind for future reference


Thanks for keeping us informed. That's what I like about this forum. You can learn so much about dirtbikes and what can go wrong!

My 99 WR400 is has the same symtoms as yours, but it doesn't have the AIS. I wonder if I have a vacume leak somewhere?

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