Gas-oil mixture: 25 to 1 ratio
Use any commercial 2-stroke oil, or SAE 40 (that's what Harley 2-stroke oil was)
5.1 ounces of oil in 1 gallon of gas
Spark Plug: Champion H8 or H8C
(Autolite 216, AC 43LS, NGK 36L are similar)
Spark Plug Gap
Battery ignition: .025 - .030 (Model 125 and Model 165)
Magneto ignition: .040 - .045 (Hummer, Super 10, Pacer, Scat, Ranger, Bobcat)
Points Gap
Battery ignition: .020
Magneto ignition: .018
All models: Disconnect the spark plug wire before pushing the starter crank to get the points on the high point of the cam - it might just start !!! Better yet, remove the spark plug to make it easier to rotate the engine to get to the high point of the cam.
Magneto models - The upper set of points powers the ignition. The lower set of points powers the stoplight. The cam has two lobes, so you'll have to get the ignition points on the high point of the ignition cam. Later, get the stoplight points on the high point of the stoplight cam.
The points need to be cleaned periodically. Use a points file, a piece of 240-grit Wet-or-Dry sandpaper, or in a pinch, the striker from a book of matches. If the points are pitted - and they probably are - you should remove them and clean them up on the bench. If they're badly pitted or burned, it's time to get a replacement set (and get a new condensor while you're at it).
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The Service Manual contains complete dis/assembly instructions. If you don't have one, you really need one. Harley Part# 99444-93 is available from your local dealer. $40 gets you a Service Manual, a Parts Catalog, and much much more.