Did you clean both faces..?
Did you tighten cylinder head bolts in sequence..?
Did you check the valves and valve clearance..?
And have you done a compression test..?[
I just thought of the one thing that I did not question. I purchased a used cylinder head, after we had it running and putting the sheet metal, I noticed that the head we where putting on had the spark plug hole in a different location. Could this have something to do with it. Otherwise everything else was done by the book. I am currently in the process checking coil to make sure it is the right[made in china brand]