I recently had a fresh valve job and new valves put in my bbc

After about 10 hours of use
I noticed a drop in performance.
I performed a leak down test and found out I had a bad burnt intake valve.
 Pulled the head and confirmed the intake valve/seat let gasoline come out when poured in intake.

Jetting is correct
Timing is set at 32 total
Never gets above 150 degrees
And has about 4 psi water pressure at idle.
It’s a hydraulic roller motor and valves were lashed correctly 
Any one know of another reason the valve could get burnt ?

Thanks for any help