1970 Johnson 20HP (20R70E) More Power Please

H

Hodie

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I have a 20R70E Seahorse. Oldie but a goodie... but getting less and less performance. I was passed by 15HP... :( LOL, but newer model so rated at prop not head.

I have read many post about "converting 20HP to 25HP (or even 35HP)" but they all seem to be late 70's or early 80's models. Can a 1970 20HP be converted to a 25HP? a 35HP? I'm sure it can be, but how?

Any help????
 
T

tx1961whaler

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Re: 1970 Johnson 20HP (20R70E) More Power Please

Go to http://shop.evinrude.com and check out the electronics parts catalog.
It appears that the only difference between a 20 and 25 hp in 1970 is the carb. and cylinder head. The intake manifolds are the same, as is the powerhead PN, but the cylinder head appears to be different.
If you had a free 25 hp donor to take parts off of, it might be worth playing around with, but I wouldn't spend any real money to get maybe 5 hp that you probably wouldn't notice.
 
samo_ott

samo_ott

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Re: 1970 Johnson 20HP (20R70E) More Power Please

Lighten the boat? Balance the load?
 
CATransplant

CATransplant

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Re: 1970 Johnson 20HP (20R70E) More Power Please

First step is to figure out why you're getting less and less performance from that outboard. Sounds like it's time for a thorough carb cleaning, decarbonizing, and tune up. If it's not performing like it used to, you need to fix it. Is the prop all beat up? Get a new one. Fix the outboard you have and it will perform like it used to.

Did the guy with the 15 hp have the same boat as yours? If not, there's no way to make the comparison.

If it still isn't satisfactory, put an ad on Craig's List. Sell it. Then read the ads on Craig's list and buy a 25 or 35 hp outboard. It'll be the cheapest possible way to upgrade your performance.
 
tashasdaddy

tashasdaddy

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Re: 1970 Johnson 20HP (20R70E) More Power Please

check your compression and spark also.
 
Chinewalker

Chinewalker

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Re: 1970 Johnson 20HP (20R70E) More Power Please

20 and 25 are very different motors. The 25 had different pistons, cylinder head and crankshaft, plus a differently jetted carburetor. Converting a 20 to 25 would require either a complete rebuild using 25hp parts, or simply finding a 25hp powerhead.

The crux of your issue seems to be you feel you're losing steam. If that's the case, there's a good chance you're not getting your original 20 ponies. Compression, link & synch, prop selection & set-up all need to be addressed...

- Scott
 
H

Hodie

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Re: 1970 Johnson 20HP (20R70E) More Power Please

WOW... I can't believe how fast you guys jumped on to help. THANKS! This old Seahorse is a keeper. It's a "Icon" amongst my trout fishing buddies (they all run newer 9.9's and 15's) and I have always run circles around them. I am hoping the problem is "fuel" or the lack there of. I have always had a small leak under the hood and not sure where it's coming from. I will clean and rebuild the carburetor, get a new fuel pump kit and replace the fuel lines. I will let you know what it does. Hate to think about the electronics end of it... that stuff is "sparks and magic" to me. Thanks ALL.
 
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