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1978 Johnson 70hp Intermittent Firing on One Cylinder

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wayne

New member
" I have a 1978 70hp 3-cylind

" I have a 1978 70hp 3-cylinder Johnson that starts fine, but once warmed-up after 5 or 10 minutes, it starts mis-firing on the lower cylinder. I have installed new spark plugs and replaced the lower ignition coil. Any suggestions??? "
 
Check your compression..Inspe

Check your compression..Inspect the lower plug for any signs of moisture..Possible headgasket..
Gary
 
" Yes I would do a compression

" Yes I would do a compression test on it. I had the same thing happen to me with a little 4 hp twin, started up fine and idled great until it warmed up after a few minutes. If I started it up and just took off from the dock it would go great for about 100 yards and then start to miss and eventually died out. My first thoughts were bad gas or water in the gas. turned out to be the head gasket. Would have saved myself a few hours of frustration and wasted time if I had of checked compression first. "
 
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