[Masteryota]

Ok. Sounds like a few possibilities. Timing sounds like it is off, or the valves are not adjusted correctly, holding them open too long. That being said, these are 'interference' engines, meaning if the timing is off too far, the valves will hit the top of the piston.

I believe the head can only be installed one way, with the cam chain coming through the head.

I would check to see if the valves are too tight, then report back your findings.