2009 yz450f won't start, flooding itself

Ok so I just bought this 09 yz450f. It's super clean and ok hours. Its had a recent top end including valves. It started 3rd kick when I was looking at it, and ran like a champ. I rode it also, plenty of power, and it didn't bog/want to die. There weren't any backfires/signs of valve clearance problems either. No abnormal sounds, ticks, ect. I drive the 2ish hours home, unload the bike, and now it won't start. It keeps flooding itself... so I take the tank, ect. off to get to the spark plug..and its wet as shit. I dry it off, wire brush it, and blow air into the combustion chamber to evaporate the fuel. Then I test the spark and its strong and blue. Then i put everything back together to find that within a few kicks the bike is backfiring and popping as I'm trying to start it. I am giving it zero throttle as I kick it also. It ran perfect before I hauled it home..and there is no way at all that it could've jumped timing. So I'm stumped. Probably going to tear it down after school tomorrow. Im thinking it could be a stuck float/needle valve..? There isn't any gas pissing out of the carb vent lines though. Thanks for everyone's help.

If you've got the tank off, you're only about 2min away from having the valve cover off to check the timing... I just bought an 07 that I rode once, stalled and wouldn't start. Got it home and found the exhaust cam about 40 Deg out. Just bought a new chain and it was visibly shorter than the old one...

Well it just had a top end done.. I've done a little thinking and I think that loading the bike in the truck caused the float to get stuck..it always used to happen to my brothers 1998 yz250 so the first thing I'm gonna do is pull the fuel bowl and see if the float was stuck

Mine was at 17hrs on a new top end. PO's shop didn't replace the cam chain. I'm with you on the stuck float, but like you said, it should have been dumping fuel out the overflow if that were the case... My old KX leaves a nice little puddle in the truck if I forget to close the petcock...

Well I pulled the fuel bowl and found that the float was stuck. I flushed it out with some carb clean and it's free to move on it's own now. I haven't tried to start it yet though, going to get some o rings for the fitting the fuel like goes on to..it was leaking aswell. This top end has about 4 hrs on it. The pervious owner was very good about maintaining the bike...dates and hr. points are written in the back of my manual for everything he's done to it. And same with my old kx..I had a 500. Fast as &%$#@!.

Good luck, hope that does it... I've got an old KX250, but if I ever get to the point where I can have a bike just for Glamis, a 500 is on my list. That actually gives me an idea - they're both green and my wife can't tell a KX500 from a Ninja500, hmmmm

Kx500 supermoto and just have a spare set of tires hahaha

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