1970's 6 hp johnson

J

jsepp

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Sep 27, 2004
Messages
2
Hello, I have a 6hp johnson not sure of the year. I think its a mid to late 70's model.Ever since my grandpa owned this motor it ran kind of funny. When you have it wide open it kind of bogs down,so a couple of weeks ago I tore the carb apart and cleaned it. I put it back together and it still does it. Then I discovered when the cover is off the engine it runs like a million dollars. So I think it is starving for air What is the problem? How can I fix this? Thanks
 
R

R.Johnson

Rear Admiral
Joined
Sep 24, 2003
Messages
4,446
Re: 1970's 6 hp johnson

It sounds like you are pulling exhaust gases into the hood. I have seen where this can happen when trying to run the engine in a barrel, or tank. When running on a boat, air flow will carry the gases away.
 
Chinewalker

Chinewalker

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Joined
Aug 19, 2001
Messages
8,902
Re: 1970's 6 hp johnson

I had this happen on a similar motor. Someone had replace the plug wires at some point with a set a few inches longer than original. Motor would run fine with the cowling off, but would drop a cylinder with the cover on - the bottom plug wire was getting caught in the rear latch and grounding out...<br /><br />If that's not it, definitely follow R.Johnson's suggestion on checking the gasket between the powerhead and the exhaust housing. Depending on the model year, some need the powerhead pulled to access the shift rod disconnect, which can lead to a chewed up gasket if it isn't replaced...<br /><br />- Scott
 
J

jsepp

Recruit
Joined
Sep 27, 2004
Messages
2
Re: 1970's 6 hp johnson

I went out and messed with it and it seems like its really rich with the cowling on. When I take it off alot of the smoke goes away. If there a air mixture screw on this thing?
 
fireman57

fireman57

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Joined
Aug 24, 2004
Messages
3,811
Re: 1970's 6 hp johnson

Sounds like you have an exhaust leak in the donut where your powerhead sits on the lower unit. It lets exhaust in the cowling and the engine does not get the clean air it needs to run. Check at the base for black sludge or deposits and it should tell the story.
 
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