Last point to keep in mind. Hopefully this will answer your questions as well. The vacuum advance and mechanical advance do different things to create the advance. The mechanical uses weights and springs to advance the rotor beyond where it would normally be, in relation to the driven shaft. The vacuum advance actually moves the breaker plate, or in electronic ignitions, the pole plate, where the magnetic ring is. Both forms of advance work independent of each other, and must be added together when determining your total advance.
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