Or you could look in the manual and use what Yanmar recommends.
Your mechanics method does not factor in an incorrect prop or any of the other problems that can limit RPM - you'll just run at 80% of an incorrect RPM.
Then why does Yanmar say "full throttle" in the manual?
My 2GMF has a lot of trouble starting other than WOT.
So did my other 2GMF
So did my 3GMF
So did my YSM8
Full throttle till it lights then pull it back.