2007 yz450f wont start need help!

Ok ive been at it for a week on this thing. It won't normally start. But the weirdest thing is it will only start if I take the tank off flip the bike upside down and getting all fuel out of the bike. Then 8 kicks or so later it start up for about 10 seconds and shuts down and won't start back up. So back story. A year ago I dropped it well running it up a ramp and it skipped a tooth on the timing. It sat for a year and last week I fixed the timing changed the oil and oil filter and changed the gas out. Still wouldn't start. So I took the carborator apart and cleaned it and replaced the fuel line.. still wouldn't start changed the spark plug checked for spark that was good. Still wont start. So that's when someone recommended making sure all the old fuel was out. So idk I was sick of this thing and wanted every drop of fuel out of this bike. So I took the tank off and put it in first, grabbed the handlebars and put it upright on its back tire then upside down. Pulled the throttle a bunch and got all fuel out of the carborator and motor. Put it on both wheel and it started up! Didn't sound the best but it started and lasted 10 seconds. I stopped it and waited a bit and it wouldn't start again. No matter what I did.. so whatever I flipped it over again and and drained it. And it worked again! Same thing 10 seconds turns off won't start again. Any ideas? Anyone please!!!!!

The air filter seat all plastics were off during the whole flipping of the bike

I clean them by passing the correct sized number drill through them as described in that link.  The passage above the pilot jet and the passage above the fuel screw run vertically until they intersect the passage running horizontally back from the pilot air jet at the mouth of the carb.  The area where the three intersect is subject to blockage also. 

Well I cleaned it out pretty good it seems. Do you replace them or clean them out?

The key for me is letting jets, carb parts etc sit at least 24 hours in carb cleaner. I usually use a mason jar. Then I take compressed air, blow them out and then spray some more cleaner to make sure everything got out. I cleaned a 1996 yz 125 carb that everyone said just buy a new one. I would check your timing once again but it still sounds carb related. Worst case buy a rebuild kit.

The key for me is letting jets, carb parts etc sit at least 24 hours in carb cleaner. I usually use a mason jar. Then I take compressed air, blow them out and then spray some more cleaner to make sure everything got out. I cleaned a 1996 yz 125 carb that everyone said just buy a new one. I would check your timing once again but it still sounds carb related. Worst case buy a rebuild kit.

 

Never put a four stroke carb (Keihin FCR MX) in a parts cleaner tank, though. Too strong of a solvent.

You will destroy the inner body seal, ruining the carb unti you replace it, which is a real pain....

Never put a four stroke carb (Keihin FCR MX) in a parts cleaner tank, though. Too strong of a solvent.

You will destroy the inner body seal, ruining the carb unti you replace it, which is a real pain....

To clarify I buy the $3 can of carb cleaner from Walmart and soak only the jets and whatever other metal pieces that could be clogged. I would soak the entire thing :p

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