25 hp evinrude, power increase

[squid121]

I have several 18 and 25 hp Johnson and Evinrudes from the 60's and 70's that I've torn apart and completly rebuilt where needed, and although they all are running pretty good, ( good comperssion, points set, new coils,carbs cleaned and rebuilt) none of them have the power of my last 1978, 18 horse evinrude which is blown. in fact the 25 hp don't seem to have any more power than the 18's. I read the posts about the fellow who converted his '88, 20 hp to a 35 ish hp. My question: is there similar possibilities with the 18 and 25's from the seventies? and if so where can I read up on it. Thank you

 

[G DANE]

Re: 25 hp evinrude, power increase

Sorry, I dont think it is possible. The 18, 20 and 25 HP motors up to 1974 all had the almost identical fine 22 CID displacement powerhead. The 25 had different crakcshaft, pistons and cylinderhead, as I remember. The 25 HP needs to turn 5500 RPMs to put out 25 HP, if it isnt set up with a propeller that makes is possible, it will perform like a 18 or 20 HP. The 35 twin that came out in 1976, at first, had 38 CID powerhead as far as I rember. In the first years there were lots of differences between the different horsepowers, from around 1985 most of the detuning was in the carb and intake.

 

[squid121]

Re: 25 hp evinrude, power increase

Thanks for the info. I need a quick lesson on props, What would you suggest I use for this scituation?