Help with replacement prop, 1998 755 HP Force, pontoon boat

[Joe Friday]

I am in the process of working on an old 1976 28ft Aloha pontoon boat. I recently found a good deal on a 1998 75 HP Force outboard. The engine came off of a 18ft pontoon that had been used on a river and the prop is in pretty bad shape. I have had the new boat/motor combination on the water once, and even with a beat up prop, the old Force would push the boat at 15MPH (checked with the GPS on my phone) with four adults and two grandkids on board.

Now that I now there is a chance that the engine is worth spending some money on, I am interested in replacing the prop, and probably adding a tach. I have spent most of the afternoon looking for info on calculating prop size, but have come up empty.

The old prop is marked "F10.63 X 12P" I have not found and indication what this is, but am assuming it is a 10 X 12 prop. From the center of the hub to the tip of the blade measures about 5 1/4 inches.

I know I need to adjust the prop for the larger boat, but don't know what I should be looking for.

The motor had not been used for about the last three years, and seemed to start missing about at about 3/4 throttle. Any thoughts or suggestions welcome.

Thanks!

 

[ahicks]

Prior to buying your new prop, my focus would be on getting the engine running to it's full potential, then installing the tach you mention. At that point, you can use your current performance to make a very educated guess on what prop you need.

Regarding the miss over 3/4 throttle, first guess would be a fuel delivery issue. It's running out of gas at 3/4 throttle. Why is anyone's guess. Could be anything from a plugged intake inside the gas tank, to leaking fuel line connectors sucking air, plugged filter, bad fuel pump, plugged jet(s) inside of the carb(s). Start by eliminating the easy stuff first....