Questions on converting 1991 Johnson 25 HP to 35HP

[TaylorMann1]

I recently picked up a 1991 Johnson 25 HP that was made in Belgium. The midsection of the motor appears to be the same as the 30/35.

I'm hoping someone on this site has done this conversion before and could provide a little bit of insight.

Looking at parts diagrams I believe all that I need to change is two orifice plugs in the carburetor and the intake manifold. Does anyone know any other differences?

Thanks for any help in advance!



ORIFICE PLUG (#39). 30 & 35 MODELS ONLY - Part # 334568

ORIFICE PLUG (#65D). 30 & 35 MODELS ONLY - Part # 327541

MANIFOLD, INTAKE. 30 & 35 MODELS ONLY - Part # 396790

 

[TaylorMann1]

Doing more research I found that the 35HP carb has a much larger throat, therefore I cannot just re-jet my existing carb. This was comparing a 1988 25HP and a 1984 35HP intake and carb.

I believe they used the same carburetors from 1984 to 1995, can anyone confirm if this is correct and if all of the years listed used a primer system?

If anyone has a 35HP intake and carburetor let me know!

 

[Tim Frank]

There are myriad threads in here that start "how do I change a ___HP to a ___HP?" They are almost always a long sad story.
The best advice that I've seen is that the most cost effective way to convert a 25 HP to a 35 HP is to sell the smaller motor and buy the bigger one.