# Changing Johnson 25 hp to a 35 hp??



## alain_vallejo

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.


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## blondmonkey777

Wheres the easiest place to find one of these?


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## Dadvocate

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


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## firecat1981

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


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## Creek Runner

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.


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## blondmonkey777

Its a 2005 what would have to be on that year model to upgrade hp and how much hp would you really gain? thanks for all the info


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## Creek Runner

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.


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## blondmonkey777

Im using the 25 hp because I need a light weight motor im pretty sure that making a 2005 johnson 25 to a 30 is what just a different carb?


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## Creek Runner

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


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## blondmonkey777

alright thanks


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## el9surf

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


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## Dillusion

> 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


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## blondmonkey777

No I dont have the built in fuel tank but I wouldnt mind the extra 5 hp lol


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## jzs702

blondmonkey777 said:


> Its a 2005 what would have to be on that year model to upgrade hp and how much hp would you really gain? thanks for all the info


I know this is a pretty old post but did you end up doing this? If so, how did it work? I have the same 05 25hp and just came across a 30hp carb. Just curious if it was worth it and if anything else was involved.


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## JC Designs

jzs702 said:


> I know this is a pretty old post but did you end up doing this? If so, how did it work? I have the same 05 25hp and just came across a 30hp carb. Just curious if it was worth it and if anything else was involved.


You will probably need the reed stops and maybe the exhaust tuner from a 30 to see any real gains. You can go to boats.net and cross reference said parts between hp’s.


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