'77 Johnson 70 losing cylinder

CFORBERG

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Aug 21, 2005
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My 1977 Johnson 70hp triple is not firing on the bottom cylinder.<br /><br />I cleaned and kitted all 3 carbs, no change. Compression is 120 on all 3 cylinders, and all have spark. The spark is not super strong, but is the same on all three.<br /><br />Bottom plug gets wet fouled (new plugs, gapped .040). Little or no suction from bottom carb. I shot pre-mix into the carb-no change.<br /><br />I physically checked to reed valves (through the carb opening) and they seem clean and functioning correctly.<br /><br />The motor will stall when accelerated, but will eventually take off after idling around for a while. I had a similar symptom last year, and discovered water leaking into the bottom cylinder through the exhaust port due to a bad gasket. Replaced gasket, problem solved (until now!).<br /><br />Thanks in advance for your help!<br /><br />Clint
 

CFORBERG

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Re: '77 Johnson 70 losing cylinder

Also, I did sync and link the carbs and ignition system.
 

Walker

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Jun 15, 2002
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Re: '77 Johnson 70 losing cylinder

What sparkplugs?? I think those 3 cylinders run best on L77JC4's gapped at .032
 

CFORBERG

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Re: '77 Johnson 70 losing cylinder

I'm using QL77JC4's gapped at .040.<br /><br />Forgot to mention that fuel pump and all hoses and clamps are new.
 

Walker

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Re: '77 Johnson 70 losing cylinder

If it was mine I'd gap the plugs at .032 and I'd clean all three coil grounds and the block where the ground at. Then give her another try.
 

CFORBERG

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Aug 21, 2005
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Re: '77 Johnson 70 losing cylinder

Thanks, Walker, for the good advice...I'll try that this weekend. Does the bottom cylinder typically "load up" more than the others? Am I just losing spark to a fouled plug?
 

CFORBERG

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Re: '77 Johnson 70 losing cylinder

Is it possible to swap ignition coils to see if there is a change? I'd like to test before buying new parts!
 
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