Phil
Not really understanding what you are referring to with the gaskets… I don’t really understand why they need the two different gaskets for the (1956 and newer) non thermostat vs thermostat models. It sure looks like the 313065 in your first picture was packaged incorrectly….LIke you said, the 313065/thermostat models gasket usually has the small hole in it, the one in your picture seems identical to the 304314 gasket in your picture. All I know is that substituting the 56-58 and thermostat gaskets for the 303467 gasket and vice versa will result in a cooling leak under the powerhead….
GF Your description confuses me also. First off, please know that the engine must be buried deep in the water when running in a test tank, the water level needs to be up and over the gearcase to exhaust housing joint (where the four bolts are). Trying to run the engine at high speeds in a test tank can cause cooling issues because of the turbulent water/air swirling around….But, seems like you report the engine only pumps when the throttle is up high. Did the water pump work correctly with the original powerhead?? If so, I am still worried that you may have a mismatched powerhead/gasket situation…Your engine uses powerhead gasket: 303467, the gasket on the right…Using either of the other gaskets will result in a cooling leak under the powerhead. Are you sure your replacement powerhead is from a 1955 or earlier model? Perhaps the ID plug is still on the powerhead, post the model number here if it is there. The ID core plug is on the right side of the powerhead down next to the base gasket.
OK, so you have not replaced the impeller. Please know that no sealer is used between the aluminum impeller housing and the SS impeller plate…Using sealer here will result in the sealer ooozing out into the impeller cavity diminishing impeller performance. Yes, this surface needs to seal properly, but cleaning the smooth SS plate and the impeller housing mating surface should offer good sealing on its own…Needless to say, if these mating surfaces are damaged/gouged/corroded, sealing will be affected, and the offending part(s) should be replaced. The SS impeller plate should not be grooved excessively where the impeller spins, same goes for inside the aluminum impeller housing. Replace these parts if they are worn excessively…
All that being said, the surface between the aluminum upper gearcase bushing/seal housing and the bottom of the SS impeller plate should be sealed…The OMC type M/ 847 sealer should be used here, or something similar. Needless to say, if the mating surfaces are damaged/gouged/corroded, the water pump will suck air instead of water, the damaged pieces should be replaced.
I would definitely pull the powerhead again, check to make sure you have the right powerhead and gasket. Once the powerhead is off, I would removed the gearcase and inspect the impeller housing and SS plate…Replace the impeller using an OEM piece, I have heard some negative feedback about the aftermarket stuff…
Once everything is apart again, feel free to post pictures if you have any questions, do so before reassembly. Don’t feel bad, I’m having a fight with a 6hp now, this will be the third time I have had to remove the powerhead and gearcase…This bugger is a fighter for sure!
