1976 Evinrude 25HP.

[phatspeed7x]

This is my 1976 25HP Evinrude Tiller mounted on my Sea Nymph FM 141. It's been a great motor season after season. I've done nothing to it but spring tune ups (spark plugs, and a half can of sea foam).

I was woundering how I could get a little more speed out out of it. It's running the stock 9x10 prop. I see that michigan match makes a 9.25x11 prop. Would I see any noticable change in speed? Loaded with just me in the boat I can hit a top speed of about 24mph according to the GPS. The boat is only 285, and with me a gear maybe tips the scale at 490-500lb.

The transom is 16" high, but the motor is a long shaft so I modified the transom to measure 20".

 

[BoatBuoy]

Re: 1976 Evinrude 25HP.

You might play with motor height some more. The only way to know for sure how any prop is working is to use a tachometer. If the prop has too much pitch and keeps the engine from attaining maximum RPM, it could cause damage. Get a TinyTach at tinytach.com for about $37 and know for sure.

 

[phatspeed7x]

Re: 1976 Evinrude 25HP.

Ok, what motor height is idea for a Long shaft Evinrude? I thought the general rule was 15" short shaft, 20" long shaft.

 

[F_R]

Re: 1976 Evinrude 25HP.

That is the general rule. Beyond that, it is play with it and see what happens. Get it too high and it will ventilate. Then when you get a belly full of that, put it back down some.

Personally, the key word was "noticable". I dunno, can you notice a mile or two per hour if you leave your GPS at home?

 

[phatspeed7x]

Re: 1976 Evinrude 25HP.

My motor has the small pin drive lower unit. I think they ran this design til 77. What was the first year of the thru hub exhaust motors? I know you have more prop opitions with the thru hub exhaust motor. Maybe I should at getting a little newer tiller with the larger lower unit. How much difference would there be between like a 25-30-35HP. Would it worth finding that couple extra HP???