Mercury 90hp jet

[Ltneid]

1994 Sea Rayder with a 90hp Mercury outboard top driving the jet impeller. Wife just bought it, and would not go over 10mph. PO said it did it on him, he changed the plugs, and it flew. I put new plugs in, and it flew about 5 minutes. I'm thinking the plugs are fouling, but don't know why.
Any ideas?

 

[racerone]

Would that be a FORCE power head installed inboard on a jet boat.?-----Do a compression test on it.