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70 johnson idle very rough dies when at low idle

T

tcalhoun

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" I have a 1978 johnson 70 3 c

" I have a 1978 johnson 70 3 cylinder and it has idled
rough for te past 3 years I have tuned it up with
new plugs, rebuilt carbs I have 3 new coils on it
a new fuel pump and the compression is around 120
on all 3 . I did all of this work in the last couple
of years . boat was in rough shape when I got it.
I think it could be the reed valves, it also gets
a miss right before the engine smooths out at high
rpm. any ideas I would like to resolve this.
thanks "
 
"Assuming the compression is a

"Assuming the compression is as you say, and the spark will jump a 7/16" gap at cranking speed (with the s/plugs out), I would double check the carburetors and make sure all of the passageways and fixed jets are perfectly clean.

Also, there is a scribe mark on the cam that slides against the carburetor roller. The throttle butterflies should just start to open when that scribe mark is dead center with the roller, not a fraction of a inch before.

Joe
"
 
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