94 200 loss of rpm

[jdh]

engine runs great for 5-8 minutes then drops to 4600rpm

[boats.net]

It could be a ignition or fuel problem. Try using a different fuel tank. If it runs ok on that fuel tank then the problem is in fuel lines or tank in boat.

[jdh]

tank and fuel fine what next?

[jb123]

IF you trust your tank-side is FINE then clean your carbs.
what is the normal running rpm before the drop ?
when is the last time you changed fuel pumps?
changed plugs ?
changed filters?
SOUNDS like your fuel supply is being cut short, as in clogged tank vent,pickup screen, air leak.