Engine Will Not Start / High Pitch Exhaust

I was riding just fine when the engine bogged down and died. I checked the usual carb settings and everything seemed to be fine. When I tried to start it up again it sounded much higher pitch in the exhaust and wouldn't start. I have taken everything apart, cleaned it and checked for leaks. I have spark and gas, there is air flow comming from the exhaust but it still won't start. Seals look good. I am lost as to what to do now. Any suggestions?

The exhaust is fixed/welded together, no parst to adjust. I soaked the muffler in de-greaser and washed out a few particulates. The high pitch sound is louder now... and it is present with the muffler removed. Still no engine start, hmmm... where next?

The high pitch noise is more of a squeek with the muffler off, if that helps. Sounds like the piston is squeeking as it moves... I just checked spark and fuel again, it's got both.