Changing Johnson 25 hp to a 35 hp??

I would look at the parts diagram, all the numbers and compared all of it. I did it to a yamaha 9.9 and made it a 15 all by changing the reed restrictor plates.

 

http://www.marineengine.com/ they have good diagrams and good service

 

http://forums.iboats.com/johnson-evinrude-outboards/converting-20-hp-johnson-35-hp-274566-2.html

 

What year is your motor? Pre 95 only thing that needs to be changed is the Carb & Intake. In 96 and later it was an entirely different block assembly. Just an FYI it's not going to make much a difference I have done probably 50 conversions and your talking .05 shaved off your hole shot and maybe 1-2 mph increase on top speed, although it does tend to idle better.

 

It's an entirely different block assembly; you would be better off buying a 35hp then trying to convert that one. I’m actually friends and worked for the engineer who designed the OMC 35hp. And as I said in my previous post you’re not going to realize much gain, the guys who say otherwise are also the guys who think that a K&N filter makes their car/truck faster.

Look for a 40hp if you want more performance.

 

Yes the 25hp to the 30hp is only the carb, the 35hp is when the block assembly changes.

 

Just for reference my 25hp at wot starts to overpower the shadowcast anyways. Not sure more hp is going to help things.

 

Did you have the built in bow fuel tank 8gal? I rode on skinny dippin's shadowcast during the ankona weekend and we were fine with the 25 at WOT