40C leaking around engine base?

[nfs1]

Having performance issues with my 40C. Idles fine but slow to accelerate and not reaching the rpms it should wide open. I've played with props and engine height, checked timing, cleaned carb and have gone through the fuel system. My boat is a light 16ft aluminum console. Got a tach installed. Should fly but only reaching about 4800rpm. Can hear a whistling sound when accelerating that seems to be coming from the motor. Noticed oily residue around engine base seal and gasket so pulled the head thinking a leak could be throwing off the mixture. How do you tell if the crank oil seals are bad? Would rather not replace them unless I know they're leaking. Hoping just a bad base gasket. Have not checked ignition system other than spark gap tester which seems to jump fine. Compression is strong and the same on both cylinders.

Cleaned up most of the oil before taking pictures.

Thanks

 

[nfs1]

Update: while waiting for replacement gasket I put my M30A3 on the same boat. It accelerates much faster, has higher top speed than the 40C and reaches correct wot rpm. So problem must be 40C. Will continue updates even if no one has any input.

 

[racerone]

Put some oil into the lower crankcase.----See if it pours out the bottom seal.-----Hard to tell but in picture #3 the seal looks iffy in the 6:30 / 7:00 o-clock area.

 

[nfs1]

Parts came today so I went ahead and removed the two seals. Fortunately they came out very easily. The right angle screw driver worked like a charm to pry out the shaft seal and for the crank seal I drilled a couple small holes and carefully screwed in two fine thread metal screws. Did the drilling upside down to reduce risk of spreading any metal scraps. The metal on the seals is very easy to drill through. Then pried out with a lever and small chunk of wood. Will tap in new seals with plastic pipe or something like that. I'll report back after sea trial.

 

[nfs1]

Well the issue wasn't fixed. The motor runs incredibly well at idle and accelerates very smoothly throughout the throttle range. The big change was I put on a new 12p solas aluminum prop and the rpm jumped to 5550. It also pushed the boat a bit faster but still it's performing similar to my M30A3 moving the boat around 30mph. So 13p to 12p prop change increased 700rpm. Regardless of being in a better WOT rpm range I should be getting closer to 34mph with the 40c. It feels about 10hp off what it should be. Again my boat is a light 15.5ft aluminum and has been tested with an M30A3.

I noticed there was still some oily fuel residue around the engine base, so thinking the leak could be at the crankcase halves. Splitting those requires removing the flywheel so I figured to try replacing engine base gasket and lower crank seal first. The leak appears to be pretty minor but maybe it's enough to cause the loss in performance. I have a brand new carb which I didn't wan't to put on and maybe send back since it was $200 but maybe I'll just try it to rule out that completely. Committed to getting this 40 to run the way it should while I have time this summer.