68 20hp carb on 25r70e

monkey box

Seaman Apprentice
Joined
Dec 2, 2010
Messages
41
I have been working on a 25r70e that i picked up for free. Motor has compression and spark. New water pump and i cleaned the carb. Upon reassembly I noticed the gasket kit for the carb was incorrect. I double checked my parts book and to make a long story short I have a 1968 20hp carb on my motor someone has replaced. It bolts up fine and all but the bowl housing is a hair smaller than what is supposed to be on there. Will this affect performance or should i just repair this carb and see what happens?
 

oldcatamount

Lieutenant Commander
Joined
Apr 4, 2010
Messages
1,740
Re: 68 20hp carb on 25r70e

There is a difference in the jets, but, if it were me, I'd use that bad boy and see if you like the performance. You won't hurt the motor, so use it.
 

James R

Commander
Joined
Feb 1, 2007
Messages
2,660
Re: 68 20hp carb on 25r70e

Keep a lookout on Ebay for the carb for your motor.
 

monkey box

Seaman Apprentice
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Dec 2, 2010
Messages
41
Re: 68 20hp carb on 25r70e

Thanks guys. I am going to test it this weekend. Before I do, how do I set the jets? Do I screw them all the way in (carefully) then back off a turn or two and go from there?
 

kbait

Commander
Joined
Nov 13, 2007
Messages
2,446
Re: 68 20hp carb on 25r70e

High speed jet (coming out of carb bowl) 3/4 turn out from gently seated. Low speed 1.25 turns out. Fine tune from there.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: 68 20hp carb on 25r70e

You'll be fine with that carb. In fact any carb that uses that same base gasket will work or can be made to work. Many times we've put a carb from a 3 cylinder motor on a 18 / 20 25.
 

samo_ott

Vice Admiral
Joined
Jun 18, 2006
Messages
5,125
Re: 68 20hp carb on 25r70e

You'll be fine with that carb. In fact any carb that uses that same base gasket will work or can be made to work. Many times we've put a carb from a 3 cylinder motor on a 18 / 20 25.

I was under the impression that on 22 cubic inch engine the 25hp carb had a larger throat than the 20hp carb? Is this not correct? I'm not sure if the 20hp carb is bigger than the 18hp carb though.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: 68 20hp carb on 25r70e

There are several throat sizes of those style carbs. We fool around with that to create more acceleration or (very) slightly more top rpm. On recreational boats at recreational rpms you probably won't notice much, if any, difference.
 
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