1975 15 hp Evinrude model 15604A Wont stay at Full Power

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RonMetz

Recruit
Joined
Apr 22, 2011
Messages
1
I have a 75 Evinrude model 15604A starts great , runs good, but under full load at higher speed, loses power, feels like it wants to kick in but wont, there is no missing or anything there is just no power after first couple minutes. I have changed coils, checked gap on plugs . What could be the problem Help?? Wanta get out on the lake for some serious fishing. :(
 
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OptsyEagle

Lieutenant
Joined
Sep 13, 2006
Messages
1,356
Re: 1975 15 hp Evinrude model 15604A Wont stay at Full Power

What plugs are you using. That motor actually prefers NGK plugs. The design of the combustion chamber seems to cause problems with Champion plugs. My motor did the same thing until I changed to NGK B7HS. With my motor you would get a surge and bog down and surge again indicating one plug intermittantly firing. Again, problem remained after multiple Champion plugs (UL81Cs) and then immediately went away and never returned upon replacing them with NGKs.

Don't ask me why. I think Frank had an explaination once about plug indexing but I can't remember the concept at this time.
 
kbait

kbait

Commander
Joined
Nov 13, 2007
Messages
2,449
Re: 1975 15 hp Evinrude model 15604A Wont stay at Full Power

Any excessive lateral armature plate movement directly changes the point gap under flywheel on '74-'76 models, causing mayhem.. More common on e-starts of the era, but check it anyway. And they can be particular about plugs, w/the low-tension magneto.. NGK B7HS were good for me too @ .030". Check your spark w/tester, ensuring that you get a consistent 1/4" blue bolt from both leads. If not, or yellow, replace points (or clean w/file.. not sandpaper!), reset to .020" and install new condensers to be safe.
 
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