Choosing the correct Tack - 2 stroke

[divco13]

The Force ( 1987 ) 150 HP that I rebuilt, runs great. Going to use 10 3/8-12.5 Prop.

The boat has no Tachometer. Is this a Point's or Electronic Ignition ?

I just want to know, the ratio of speed to Engine rpm. And to make sure after rebuild, the motor is up to it's correct rpm range.

Bob

 

[Silvertip]

You have the numbers you need to figure speed & theoretical engine rpm. A prop with 12.5 inches of pitch moves the boat forward 12.5 inches per revolution (theoretically) but in reality, due to slip (water is not a solid) there is about a 10 - 12% slip factor to consider. So - if you know the lower unit gear ratio you can determine what the engine rpm is at any given boat speed. Obviously a tach makes this much easier. I'm not up on Force motors but some of them required a special tach because of the number of poles on the stator.