no speed

[catjt98]

I have a 1974 starcraft trihull 17ft. With a 1976 115 merc. Tower of Power.....my top speed is 25mph...with two adults and two children. I have a 17px7dia. Three blade..what should i do to get more speed. Im not sure how many RPM I am running as my tach wast working at the time.

 

[jestor68]

Re: no speed

The size of that prop(if a Mercury prop) would be 13-1/4 diameter X 17 inch pitch.

That motor should be capable of pushing your boat to about 40 mph, turning within it's recommended rpm range of 4800-5300 rpm.

How long have you owned the boat? Has it always performed so poorly?

A compression test may be in order, as well as a timing check. Those motors have a cogged belt driven distributor. Some times the belt can skip/jump a notch on the dist pulley; retarding the timing. This can happen as the belt ages(stretches).

 

[steelespike]

Re: no speed

All good points ^. You might check a couple of easy things as well.Be sure all plug wires are on, be sure the carbs are opening all the way.

 

[catjt98]

Re: no speed

I havent owned the boat but about three months and I have only ran a couple tanks of fuel through it. I have checked that the carbs are opening and the throttle operates fully. all the plugs are firing. I was beginning to wonder if prop was too big. I will have to wait until spring to get it back in the water and see what the rpms are running. I appreciate all the feed back and hopefully get this figured out.

 

[Don S]

Re: no speed

What is the maximum rpm you are getting out of the motor at wide open throttle (WOT) That is the one number you MUST have.