What all is different in a 1971 25hp and a 35hp Johnson?

[hi salenity]

I just got a 1971 25hp Johnson and was told that it could be made into a 35hp by changing the carb to a carb off a 35hp. Is this true or do they have a different bore & or stroke...?

 

[Chinewalker]

Re: What all is different in a 1971 25hp and a 35hp Johnson?

No way, no hown. The '71 25 is a maxed out 22-cube block. The old generation 35s are 40-cube "Big Twin" style motors, while the later style 35s are 31.5 cubers. VERY different motors. Your 25 is a 25 and that's all it can be...

 

[hi salenity]

Re: What all is different in a 1971 25hp and a 35hp Johnson?

After looking at the numbers I don't even think it's a 25 I think its a 20? The serial # is 20r71s that's a 20 correct?

 

[AlTn]

Re: What all is different in a 1971 25hp and a 35hp Johnson?

that's the model no. for a 20 hp....yes

 

[Chinewalker]

Re: What all is different in a 1971 25hp and a 35hp Johnson?

And, anticipating your next question, there is no easy way to convert your 20 to a 25 without major surgery (different crankshaft, cylinder head, etc.).