1978 Johnson rebuild.

T

tranquility

Seaman Apprentice
Joined
Jul 16, 2007
Messages
32
While I have this motor off the boat I am considering doing some work to it. Engine runs fine now but has unknown hours on it. What would be required to up the HP a bit? New reeds perhaps, maybe carbs. Any ideas for increased performance on this engine.

Thanks
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: 1978 Johnson rebuild.

First, OMC made about a dozen outboard models in 1978. Which one are we talking about?

Second, it ain't broke so don't fix it.

Third, to get increased performance from a boat and engine package fine tuning the rigging and propping offers far better and less expensive results than messing with the engine. New reeds will work just like the old ones. Same with the carbs. Any "hop ups" will sacrifice reliability and user friendliness.
 
T

tranquility

Seaman Apprentice
Joined
Jul 16, 2007
Messages
32
Re: 1978 Johnson rebuild.

1978 Johnson 150. 20 inch shaft.

I am thinking that a new prop would be the best idea. I am currently running a 15x17 Aluminum. It makes 5400 RPM wot. Max rated is I believe 5500. However I do get some ventilation in turns with the current setup.

Would you have a prop suggestion?

Thanks
 
ezmobee

ezmobee

Supreme Mariner
Joined
Mar 26, 2007
Messages
23,767
Re: 1978 Johnson rebuild.

You're doing very well with your WOT RPM. I'd look into the same prop but in stainless.
 
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emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1978 Johnson rebuild.

The recommended stainless will hold a lot better. You may find that you will be able to move the engine up one notch on the transom and not loose bite. Less engine in the water=more speed.
 
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Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: 1978 Johnson rebuild.

5400 on todays fuel is border line lugging. Target 5800 or so as the top rpm with an average load and the motor will be a lot happier. Your performance and efficiency should increase a good bit (depending on what hull you have).
 
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