Home › Forum › Ask A Member › ’57 Johnson 7.5 hp dropping a cylinder, but got it back???
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jeff-register.
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April 14, 2016 at 9:30 pm #4038
Motor as stated, came in lost a cylinder, but ran fine prior. Looked under flywheel, on the outside of the power head and sure enough, oily mess, so I removed flywheel, and found one set of points soaked with oil. cleaned and reset points. Went to lake, once started it ran fine, but all of a sudden it dropped what would later be found out as the top cylinder. I was trying to limp back to the do\ck and all of a sudden just as I had lost that cylinder, it came back….
This motor has the slinger which by the way is all there and not missing anything. Pulled flywheel again, and points are fine…
What possibly could have caused this?
Coils look new and have an OMC number 583249 on them….it had NGK BM7A plugs in, they are now replaced with J6cYes I have a MercOtronic and no I have not checked the coils….
Losing spark would make me think coil, but getting it back without shutting the motor off baffles me..
Thoughts?
http://www.richardsoutboardtools.com
classicomctools@gmail.comApril 14, 2016 at 10:07 pm #34816Well, the spark would not have come back if wires got chafed under the flywheel. I’m confused, did you pull the flywheel to re-inspect after the engine messed up/fixed itself? If not, you might just pull the inspection cover to have a quick peek. I hate it when this stuff happens, just leaves you feeling uneasy about the repair. Could be anything, might even have been a bit of carbon fouling the plug temporarily, who knows! I guess I would try to water test it again tomorrow to see if it messes up again. If it messes up again, I would just go through everything with the mercotronic…..
April 14, 2016 at 10:15 pm #34817Yes pulled the flywheel once home, everything looks fine…finally got some boating weather here in Northern Indiana, so I have NO issues with going for another boat ride..LOL
http://www.richardsoutboardtools.com
classicomctools@gmail.comApril 14, 2016 at 10:20 pm #34818yeah, I would run the coils and the condensors on the mercotronic.
Perhaps the secondary winding is partially fractured, or shorted condenser, etc…
April 14, 2016 at 10:51 pm #34819I was thinking just what fleetwin said—a temporary fouling of a plug due to a flake of carbon flying around in the cylinder.
April 14, 2016 at 10:53 pm #34820Ok I will look at the plugs again before I head out…. Frank, check your messages bud…LOL
http://www.richardsoutboardtools.com
classicomctools@gmail.comApril 15, 2016 at 5:42 am #34832Can you hear a clicking or snapping noise while it’s running on one cylinder? If so, that could be a bad coil leaking to ground where you can’t see it. If you remove the coil, there may be a small black spot on the bottom which shows where it is leaking.
April 15, 2016 at 12:12 pm #34839Regarding spark plugs fouling with carbon chunks. When I was a kid I had
an 80 Yamaha motorcycle, oil injected, single cylinder. It was notorious for fouling
the plug. I’d be cruising along and it would start spitting and sputtering,
and most times quit all together. "Some" times it would spit and sputter
until almost stopped, then let out a mighty backfire, and I’d be back
on my way. My Honda buddies didn’t have this problem 🙂
Not sure if an outboard would exhibit similar symptoms!Prepare to be boarded!
April 15, 2016 at 12:30 pm #34840+1 on condensors. They sometimes fail under load and then come back after a while.
April 15, 2016 at 3:21 pm #34842I would clean and polish the polnts. It sounds to me that there was a contact issue there. If oil was all over under the flywheel, then it’s likely that it could still be causing an issue. You may also check the spark plug ends. Often times coils can be changed and the old wires are still in place.
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