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I like the vacuum advance feature for "cruising". At LOW rpm the centrifigal advance doesn't provide enough advance to "optimize" the burn process. Generally speaking the Vac advance will increase effeciency and thus fuel mileage in a cruise mode (light throttle, low rpm).
At wide open throttle or high rpm (race mode) there is very little if any vacuum and advance is handled by the weights. If your not interested in "cruise" mode, focus on the "race" mode and keep the rpms up.
This logic would apply to a heavily modified engine or a stock engine. Using "weights only" will provide ABSOLUTE control of the timing at any given rpm, desirable for a "race" application to eliminate a major "variable" and allow precise "tuning" of the engine. In a race application you could care less about "gas mileage"!
Ernie
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