Changing a 25 horsepower to 20 horsepower

K

ktate

Recruit
Joined
Sep 7, 2008
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I have a 25 horsepower Johnson motor. Can you change the carb to make it a20 HP.

Thanks
 
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CATransplant

CATransplant

Admiral
Joined
Feb 26, 2005
Messages
6,319
Re: Changing a 25 horsepower to 20 horsepower

Hmm...well, the cowlings are the same for the two engines of those years, so, I suppose you could put a 20hp cowling on it and forget it or even a set of 20hp decals. Trouble is, the plate on the outboard will still give the model number.

Even if you put the 20 hp carb on it, the plate would still be there, telling whoever checked the boat that it was a 25hp.

Tough dilemma. If you're going to boat primarily on the restricted lakes, you might just want to sell the 25 and buy a 20. I don't know.
 
kenmyfam

kenmyfam

Supreme Mariner
Joined
Aug 10, 2006
Messages
14,385
Re: Changing a 25 horsepower to 20 horsepower

How closely do they check the motors ????
 
mthieme

mthieme

Captain
Joined
Oct 6, 2007
Messages
3,270
Re: Changing a 25 horsepower to 20 horsepower

Why don't you just change the sticker on motor.

With Mercury, it's the same engine, one is rated for more rpm.

I thought PA had a 10 hp limit on the lakes?
 
H

hammerhandle

Petty Officer 3rd Class
Joined
Aug 21, 2006
Messages
75
Re: Changing a 25 horsepower to 20 horsepower

from a johnson repair service manual Quote " If lake or boat restrictions require a motor with a maximum of 20 hp, a Johnson Restrictor Kit can be isntalled on 1977 and earlier 25 hp models. this low cost kit is installed behind the carburetor and reduces both power and fuel consumption. The kit is available at your dealer.------- not sure if they make them for your year but may want to try a dealer , my repair manual is from 1982.I would also contact the DNR for Penn.and see what there take would be on it since its so close to a 20 hp. you might be able to retrofit something too.just my 2 cents. cheers !
 
samo_ott

samo_ott

Vice Admiral
Joined
Jun 18, 2006
Messages
5,125
Re: Changing a 25 horsepower to 20 horsepower

Wow. first time I have heard of someone trying to lower the hp of their engine, most folks want to up it all the time. That's good of you to be so diligent.
 
frustratedboater

frustratedboater

Chief Petty Officer
Joined
Jul 10, 2007
Messages
413
Re: Changing a 25 horsepower to 20 horsepower

That is unique! I had to change powerheads on a Evin. 30hp to 35hp (with minor fabrication it's a sleeper!). If I'm quoting Chinewalker correct, If you change the cyl. head, that drops the compression ratio, which in turn, drops the hp rating.... All that's not worth it. Between decals and heads, it's just a "headache"

~FB~
 
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