Re: 1996 120 mercury Sprt Jets
Where is your hose hook up at the fat hose coming from the jet drive or on top of your thermostat housing?
you need to use the hose hookup that adapts to the engine cooling hose and make sure the water pressure is only about an 1" above the hose when the hose is held vertical facing up else you will flood the bottom cylinder. You should only run it at idle on the hose for short period of time and always turn on the water before you crank it.
The previous owner probably made the mistake of starting it up on the trailer without any water flow.
The water washes away the fuel that accumulates in the exhaust while cranking, without water flow, once it engine starts it causes a backfire and the pressure from the explosion can and will blow or bend the ride plate or seal, its a pretty stupid design on mercury's side.