After he finished overhauling the carburetor, we learned that one of the dead engines had a race engine piston cylinder. It was additional work but I could not stop him from pulling the the exhaust pipe and swapping piston and cylinder. After swapping the the engine cylinder and piston, we fired up the bike and it started almost instantly then we found out that the clutch discs were sticking so he had to open the the gear box cover and pull out the clutch discs. The clutch disc holder was not in good condition so he had to open up another engine to salvage the part.
Damaged clutch discs.