[lippy]

Originally Posted by cycleguy55

It's simpler - one less thing to worry about.

OTOH, distributors with vacuum advance also have mechanical advance.

Mechanical advance is controlled by weights on springs, spinning on the dist. shaft. They advance timing as RPMs increase. Mechanical advance is necessary if you want to rev over 2000 RPM, so it's always there even if you don't think you have it. ALL distributors have it - except those used only as signals to an ignition box with timing curves.

Vacuum advance is there purely for efficiency. It advances the timing based on engine load. High vacuum = low engine load, so the engine can run more timing with no problems and deliver better fuel economy. The round vacuum can on the side of the distributor does this. You can disconnect the vacuum line (and plug it) to do without the vacuum advance if you want.

Vacuum advance also makes the engine run cooler and provides better throttle response at most conditions.