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My mechanical advance was and still is the best method for spark control...
There is a hub mounted on the tapered end of the crank..The hub has an extension on the back side that has a ball bearing pressed on to it..The ball bearing has an aluminum ring with a sensor expxied into it, pressed on the the O D of the bearing...There is a DuBro ball mounted on the periphery of the aluminum sensor ring with a link to the rotated carb shaft that advances the spark when the throttle is opened...Simple, cheap, and linear...
This requires the carb to be rotated so that the throttle shaft is parallel to the cylinder to make connection to the throttle a straight line...Also easy...
The carb insulator is made from 3/8 G10 epoxy board...Simple, cheap, and insulates the carb from heat...
Only problem with this setup is the user..If the throttle is opened too far for starting the engine kicks back...It's impossible if the throttle is set just above idle, 2 degrees BTDC won't hurt anyone. the piston is already past TDC when the engine fires...
It weighs only a few ounces, the weight of a thin ball bearing...But since the G62 is an overweight underpowered boat anchor most flyers took the advice of some so called expert on a forum there were not enough G 62s sold to make it worthwhile...None of my good customers ever complained about the mechanical advance...It was used on all manner of conversions for many years, but when Bill got the syncro spark circuit from Ed Vollmer he had an exclusive on EI for a few years, then it became easier to just put a syncro on the engines...Easier to just connect a circuit board in series with the ignition and forget the extra machining required....

My conversions started in 1987