Expert Advice 1989 Evin 120hp Prop

[bjcampbe25]

I have a 17' 3" v-style EBKO boat with a 1989 Evinrude 120 hp. I recently moved from WI to CO and rejetted the carbs to handle the elevation. Everything runs great accept that I lost about 11mph. I am looking for advice on what prop I can use to gain some of this mph back. I currently run an aftermarket aluminum 13 1/4" x 17" prop. I can only reach about 4950 RPM at WOT with the some trim. I am not happy with this prop since it tends to cavitate when I trim. I realize that this is not the right set up currently and want to get this dialed in so that I can use 90% of the trim to reach 5800-6000 RPM. Any assistance is greatly appreciated.

I am also interested in knowing how high you can run the RPM's for this engine. Is there a way to go beyond the 6200 RPM limiter and is this worth doing?

 

[steelespike]

Re: Expert Advice 1989 Evin 120hp Prop

Your experiencing ventilation not cavitation.
Not an expert but it appears you need to drop pitch about 4 inches and if you go to a stainless it should reduce your venting problem.4 inches should put you at about 5,800.Before any prop change you may want be sure it is tuned right, carbs opening all the way etc.post will bump up then perhaps you can get a more knowledgeable answer.

 

[bjcampbe25]

Re: Expert Advice 1989 Evin 120hp Prop

Thanks for the reply. When you say drop down 4" do you mean from a 17" to a 13"? Will this affect the top end speed assuming that everything is tuned correctly? What brand of stainless do you prefer?