'78 70 HP Johnson Lost Full Power

gfestian

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May 24, 2009
Messages
6
Lightweight on the site with 1 thread to my name, deciding between CMC and PowerTrim (went with CMC).

Was pulling the kids in a tube and the motor dropped off to a 'high idle'. Pulled back the throttle, started to die, pushed it forward, high idle for a sec. I figured I was out of gas. No luck.

Pulled the cover, thin line of oil from each spark plug and noted they weren't snug. They really don't tighten down well, just turn until they stop, concerned about putting too much pressure and stripping.

So it started, it managed a slow hull speed back to shore, but not getting up on plane at full throttle.

My plans right now involve checking compression on all 3 jugs, replacing the spark plugs and checking for spark. Can anyone offer any additional suggestions for a 'when I have to' mechanic to check???

(Also, anyone have a replacement bolt for the pivot on the right side of the motor that engages the transmission. Mine was stripped, but with the cover on it held it in place enough to pivot. Yanked the cover off in the middle of the lake and watched the pivot plate flop on its cables and plop that bolt into the lake.)

Thanks to all. Kids are looking at me with big saucer eyes about Sunday on the water. I dunno if that is in the cards.
 

gfestian

Cadet
Joined
May 24, 2009
Messages
6
Re: '78 70 HP Johnson Lost Full Power

And yes, I'm going looking for similar issues in past threads.
 

gfestian

Cadet
Joined
May 24, 2009
Messages
6
Re: '78 70 HP Johnson Lost Full Power

Compression came in at 110, 100, 105, top to bottom. Bright blue spark from all 3 wires. Neighbor suggested fuel or carbs. Was running the same fuel all day, gone through 5 1/2 of the 6 in the tank. Please let me know if me and my multimeter can look anywhere else.
 

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: '78 70 HP Johnson Lost Full Power

Those plugs should be torqued down. Why do you feel they will strip?

Have you tried running on a different tank and fuel line to rule that out of possible problems?
 

gfestian

Cadet
Joined
May 24, 2009
Messages
6
Re: '78 70 HP Johnson Lost Full Power

Torqued them down. I think I was a self fulfilling prophecy. With that pivot bolt stripped I got it in my head that threads in the block were stripping. Anyway, new plugs, a bright blue spark, some new gas and I'll swap out my spare hose from the tank to the engine. I'll put it in the water tomorrow and see if I can get it up to speed. Thanks.
 

gfestian

Cadet
Joined
May 24, 2009
Messages
6
Re: '78 70 HP Johnson Lost Full Power

Torqued down and up on plane. 'It Floats' floats again!
 

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: '78 70 HP Johnson Lost Full Power

Great!

Happy Boating
 
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