SPAZBOZ, I think I have the same issue on my 230 powerplay

where was that valve on that boat ?

or maybee the fuel pump being that it probbaly orginal.

1986 ?

I would check you plugs and see how the engine is running. IE:rich or lean. It might be to rich up top. That would cause it to stop reving. Also if you changed you HP and torque, should you change you prop to match?