Originally Posted By: BrocLuno
An OMC motor (Johnson/Evinrude) of that vintage came with Champions stock from the factory. Prolly J8J or something similar.
The factory plugs were champion surface gap plugs (no ground strap) L78V, those plugs have been superceded by the 833 or 833M or 827 or 827M. With surface gap plugs they work best if you plan on running it hard across the lake all day and stopping once you get to the fishing hole. Since they are easier to foul while trolling you can try plugs with a ground strap cold to hot L78C, L82C, L86C work well. add a Q on the front of those last number for the resistor plugs.
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I suspect it has manual hi/lo jets that can be tuned with the cover off and the engine running under load. Get a service manual for the motor off eBay and have fun
The carburetors on these have adjustable low speed mixture and fixed jet high speed
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They were touting 50:1 back in the day when I was working part time in an outboard shop in Santa Cruz. Put some rings in those motors because they tried to do the factory 50:1 thing and they don't much care for it.
50:1 is the correct mixture to run in these outboards they have needle bearings at the wrist pins and crank shaft pins. They will run 6500 RPM all day with this mixture anything more than that and they WILL foul plugs while slow trolling. If you are worried just remember even the cheapest TC-W3 oil today is still better than any oil you could get your hands on in 1977.
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Have much better luck with 40:1 and any TC-W3 name brand outboard oil. I like Quicksilver oil. Can be had at Walmart for cheap enough. For first run with a new owner, I suggest a bit rich on oil for sure. Smoke never killed anybody, but just in case they straight-gassed it during demo or something, get some oil in there ... I'd pull the plugs and spray some Tri-Flow into the upper cylinders. It'll loosen rings that have been sitting and getting gummy ...
Again 40:1 is probably over-kill for this engine and will probably result in easily fouled plugs if you do any trolling. If you think the rings are gummed up do a decarb and dont be afraid turn this engine 5500-6500 RPM some years the powerband was even listed from 5500-7000 RPM so it will handle it fine if its in decent shape and running correctly.
I have run and worked on a lot of these outboards, they are solid and run very well when you get them dialed in