4.3l merc

[Keith Turner]

Engine cuts out after 30 min of mid throttle . Backfired and dies . Have to wait 30-40 min for it to cool down before it starts up . Then same thing happens .
I have changed just about everything and can’t figure it out .
Looking for guidance !!

 

[Keith Turner]

1989 sea ray Seville cuddy . 4.3L merc .