Help with prop question

[Rick paredes]

I have a 1976 Johnson 85 hp on a 18 foot pontoon. I only get 15 mph wot. I have a 13 pitch prop. What size prop would give me more mph? The tach is not currently working I just switch this engine from a 55 hp Yamaha. Can anyone tell me how to hook this up to the Johnson engine? The wires coming out of the control box do not work.

 

[steelespike]

Re: Help with prop question

I would say the 13 is close It came with a 17 in 76.
Can't help with the tach hook up but someone will be along with the info.
In the meantime check that it is running on all cylinders.Be sure the throttle is opening all the way.If your not having any venting(cavitation) issues the motor may be too low.What kind of toon?What diameter logs.Is the speed by GPS? Speedo can be off quite a bit. With good big logs and a good setup 20 to 22 should be easy.