Need some help with my '06 YZ450

My 2006 ZY450 won't start. It wouldn't start one day last fall and because it had been getting harder to start over the season I figured with 500 or so hours it had a valve or two that needed to be re-shimmed. The current piston has about 80 hours. It's getting spark and gas which lead me to recheck timing three times and that's not it. So far I've:

*Re-shimmed; two intakes went -.05 everything else good.

*New timing chain, rechecked timing then and two more times.

*Inspected valves with head off wire brushed the carbon off, springs look fine, valves seat fine.

*New Spark plug, getting good spark

*New stator from my 2009 Yz450

*Swapped out kill switch

*Removed carb, cleaned needle, pilot, main, check float, cleaned air screw.

*Drained tank has fresh gas, and yes the fuel is on.

What's left?

Edited by FriscoKLR

Take the rag out of your airbox?

If you have fuel, spark, air and compression (do you have good compression?) it should run...unless your valve timing is off, but you checked that three times. Don't know what else to suggest.

If you're sure you are getting spark and the timing is on (I assume you also verified that the TDC mark is actually at TDC), then I would try squirting a little fuel in the cylinder and see if it fires.

Does it feel like there's good compression when you kick it?

There's good compression. No rag in the airbox or plug in the tail pipe either. The index mark on the crank was lined up and TDC verified by watching a screw driver in the spark plug hole come up\down at the index mark. Going to swap carbs, then entire ignition with my '09 and then whatever else until I find the culprit.

Rebuilt this thing three times and always fired first couple kits, this one is frustrating!

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