Re: 1975 15hp Johnson question
Start by setting the points at .020 with a feeler gauge. If you want to "fine tune" the ignition, remove the flywheel. Disconnect the condenser wire and the coil wire from one set of points. Tuck those wires out of your way and attach a short piece of wire (10 inches or so) to the points where you just disconnected the other wires. Take out one of the phillips head screws holding the ignition plate and run the short piece down through the screw hole and grab it from underneath the ignition plate. set the flywheel back on loosly but engaged with the key. Hook up a multi meter (set to ohms) to the end of your short wire, slowly rotate the flywheel clockwise until the meter needle jumps, stop, look at the timing marks on the side of the flywheel and the edge of the timing plate. they should be close to lining up. If not, lift off the flywheel and either open the points a bit or close them depending on which way they need to be moved and re-try. Do the other set of points the same way. Tedious little job, but, the motor will be "in time" when finished.