need some help on yz450f

ok i got a 05 yz450f with a pro circuit pipe on it . i got for $1200 buck cuz it didnt run. we got it to start using the choke but when we turn the choke off it dies . we tryed adjusting the fuel scerw and changing the main and pilot jet but it didnt work. the main jet that was in there was a 168 the pilot was a 45 the one we have in there now is a 165 main and a 42 pilot . the fuel screw is at 2 turn. really need some help if anyone can thanks.

Replace the seal on the needle valve (or back fire plate on the slide) part #4fn-14997-00-00 also check the plate for a crack. This should solve your problem.

Hi, JustinJ!!!

Congrats on the good deal!

Justin, I don't know if you've ever had a Keihin FCR carb apart or not (they can be a little tricky the first time), so here's a link to a good article from Dirt Rider Magazine on how to get one apart, clean it, and get it back together again.....

Is everything else up to snuff on the bike? Valves within spec? Airfilter clean?

If you haven't looked already, up at the top of the YZ450 forum/thread list is a pinned thread, or sticky, called "Common Threads: Look here 1st! Mods, Maintenance, Common Issues and FAQ's". Learn to look in there; there's a metric ton of great info there. It's full of links to good threads with good answers, and I'd bet you'd probably find one that would help with the jetting on that Yamathumper.... Hope this helps ya, and Good Luck!


thanks for all the help!!!! it didnt have the o ring for the pilot screw .

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