New Cylinder Head, Now it won't start.

[davidsuserid]

I just put a new cylinder head on the bike and after putting everything together, now it won't start. The timing and intake/exhaust are correctly matched to the crank, and the bike turns over, it just won't catch. It just keeps trying and trying trying. I have tried all the suggestions on here, thinking maybe I flooded it. And I double checked the timing etc. twice. The spark plug isn't but a couple months old, and there is a spark, cause I took it out of the head and cranked it while observing the plug, and a spark was present.

Any ideas???? It was unseasonably cold the last couple of days, but it has been cold before and it still started right up, so I don't think that is it.