2004 YFZ450 Will not turn over fully

[Punk'd]

My buddy has a 2004 YFZ450 that will not turn over fully. By this I mean it turns over until it hits the compression stroke, then stalls, and then turns over a little more, stalls and so on.

- It pop starts fine.
- We just replaced the starter.
- Battery is fine.
- Applied 12 volts to the starter directly - same result.
- Motor was rebuild and runs fine (if pop started)
- Compression was raised 12:5.
- New top end (valves, springs, clearences all done professionally)
- Has a kick starter, but is very hard almost near impossible to kick start. (Only when its warm)
- Timing is spot on.
- Turns over fine without spark plug in (no stalling)

Any ideas? We are totally stumped!

[rt20ps]

Was the crank replaced. I just rebuilt a YFZ that was doing the same thing. His crank was on the way out. I could get it to start sometimes, and then it would abruptly stall. Other times it wouldn't turn over at all.

[ss440ex]

Have ya check the valve adjustment and is the auto decomp mec working correcty?