Re: wizard powermatic 12
Nice find! The Wizzie 12 is the full gearshift version and your motor falls into the 1955 model year serials:
http://www.wizardoutboardforum.com/techinfo.html
I am pretty sure your motor has the Phelon magneto, in which case it should use the same ignition components as the Mark 25. Just check it to be sure, as Mercury may have "used up" remaining Bendix-Scintilla parts on the Wizzies. It was known to happen.
Fuel mix - I run at least 25:1 in my '50s Mercs, and usually a little fatter than that. Mercs/Wizards are primarily jeweled motors and can get by with a leaner mix better than their '50s Johnrude competition, but they still need a good deal of oil to help with sealing the center main, etc.