Mark,
From the handbook (1925 edition) the magneto timing instructions are:
"Turn the flywheel around until the exact moment of closing of the exhaust valve of either cylinder is reached. The piston should then be at the outward end of the stroke. ... When the rear valve just closes the front cylinder is at the firing point, and vice versa, and the following instructions are given assuming the timing is effected when the rear valve closes (i.e. one is timing the spark for front cylinder). Place the magneto advance lever midway between full advance and full retard and turn the magneto driving wheel until the contacts are just separating, by the fiber tip just striking the upper steel segment on contact breaker. The gear can then be meshed and the magneto secured. When the spark is correctly timed for one cylinder it is correctly timed for both."
Present day riders of 2-3/4hp models may be able to offer conversion into a degrees BTDC method.
-Doug
