'1964 9.5 not running well

I recently bought a fishing boat with a '64 9.5 hp. It started reasonably easily when running it in a tank. The idle is rough, but I have not gone through the low speed setting steps I've seen on this board.

My main problem is high speed running. The motor runs great at full throttle for 2 or 3 minutes and then slows as if I have backed off the throttle. After a minute or 2 of slow running, it will speed up again, then slow again. Sometimes, applying presure to the primer bulb will cause a speed up, but not always.

Should I just replace/rebuild the entire fuel system or is there a specific area I should pay attention to? I realize this is a bit of a shot in the dark, but any suggestions will be greatly appreciated.

Re: '64 9.5 not running well

Most OMC 6 gallon tanks have two stainless steel valves at the fuel connection (2 small prongs showing). These are engaged simply by pluging the plastic fuel connector onto the tank fitting. One is a fuel valve, the other a air vent valve.

If the tank is not this type but perhaps rather a 3rd party brand tank, there is usually a screw type vent at the fill cap. If this vent isn't actuated, a vaccum build up in the tank resulting in a problem similar to what you speak of.

If the above is okay, and pumping the fuel primer bulb (acting as a manual fuel pump) corrects the problem, then you have a faulty fuel pump.

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