Re: correct tach for my 1964 650?
Seems to me that a tach which takes input off of one spark plug firing should do just fine, as you're getting one firing pulse for every crankshaft revolution; you'd just put it on the "2-stroke" setting and away you go.
Since your motor's ign is magneto-driven, it can be harder to find a tach.
One other alternative, assuming your 65hp has a functioning charging system (stator under the flywheel and a rectifier), you can get a marine tach which works off a 12-pole alternator (the marine industry standard). This tach uses the AC impulses off one of the yellow stator wires connected to the rectifier, as a pulse signal.
At any rate, that's a purty cheap digital tach and it'd work on a variety of motors. It looks like there's plenty of wire to reach the motor, and the hourmeter feature is cool, too.
HTH & let us know how well the tach works.........ed
