The 009 is a mechanical advance distributor- that means
that the advance is strictly determined by how fast the engine
turns. The vacuum advance models have, I believe, a mechanical 
advance AND vacuum advance. The difference is that the vacuum
advance will be sensitive to throtle position and load ( you get very
little pressure drop with the throtle wide open, some when the
throttle is closed at low speed and a lot when you suddenly close
the throttle at high speed. The mechanical advance distributor
can't tell the difference between high speed/open throttle and
high speed/closed throttle; or low speed under load versus at
idle. But its simpler.

	Cheers!
	Bill