2003 WR450F Only Runs with Cold Start Pulled Out - Need Help

I purchased a 2nd hand 2003 WR450F. The bike idles and runs fine with the cold start button pulled out. The moment I push in the cold start button, the bike stalls or back fires when giving gas. It looks like the bike is running real lean the moment the cold start button is pushed in. I took apart the carburetor and here's what I have as far as jet settings:

Main Jet: #150

Pilot Jet: # 45

Jet Needle Clip position: position # 4 (center)

Pilot Screw: 1-3/4 turns out from closed position

I was going to move the jet needle clip down a position or two to make the bike more rich but figured I would ask folks on this forum. What should I do?

I also noticed that I have some air leaking from where the exhaust head pipe connects into the cylinder head. Probably needs a new exhaust gasket to tighten the seal of the head pipe into the head but don't know if this air leak could be causing the bike from running with the cold start button pushed in. Again, the bike runs and idles fine with the cold start button pushed out. Please advise.


royalpilot, I'd say you're on the right track. If the bike sat for a while the jets could be plugged with varnish, especially the pilot, those ports are tiny. I know I run a 48 pilot on my '04 and it runs better. Check the jetting threads, lots of good info there!

Your current settings are on the insane end of lean, especially with the main at 150. Go look at the jetting database in the performance index sticky. You'll be much happier...SC

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