Backfire/runs rough at high RPM

[maurice43]

Leak down test results:
from 100 psi it dropped and held at 65.
No air from carb or exhaust or oil fill.
I did hear and feel air coming from behind the valves. (reminder OHV engine).
Did the test with the engine warm not hot.

compression test:
dry-70 lbs

wet-80 lbs

 

[maurice43]

Those first leak down test with 15-20 lbs are bogus. I was just shooting air in to see where it came out.

 

[Mikel1]

That's a large percentage, if it was me cylinder head would come off. I would go ahead and check the valve guides and valve seals if applicable. If that's good then set head level then put water on top of valves and using air compressor blow into valve passageways. Water will bubble out of valves if not sealing. Then get a new head gasket.

 

[bertsmobile1]

Off with the head.
65psi is way too low
and a 30% pressure drop is way too big.
Something is not quite sealing right & I would go with a failing head gasket.