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I put on a carb from a 1977 15 hp. According to Leroy's Ramblings the only difference at the time was the carb. The tuned exhaust did not happen until latter. The plate on the motor which has the model and serial numbers state an RPM range of 4500-5500 for the 9.9. I would assume for a 15 it...

I had the boat out today and the according to the timing light I was going at mostly 5100 RPM at full throttle. This gives me some room to play with, but what is the ceiling I should not go past? 5500 RPM or 6000 RPM. Also how far can I decrease the pitch for the prop and be safe? I currently...

I have a 9.25x10 prop from evinrude. If I want to decrease the prop size for a higher top end speed for a heavy boat, what size prop should I get? Background: When I modified the outboard from a 9.9 to a 15, I only gained about 2 mph. If I am overpropped to take advantage of the higher rpms...

This winter I modified a 1976 Johnson 9.9 with a 15 hp carburetor. I took it out yesterday to see the difference. Before the outboard would struggle to hit 12 mph. Now it struggles to hit 14 mph. I know the 16 foot aluminum boat is heavy with a wood floor (3 guys can barely lift it), but I...