>>Close, but not quite right. Advance should DECREASE as load goes up
>
> Surprising, that is contrary to my gut feeling and the Haynes manual
> which states that the vacuum unit is supposed to provide an additional
> advance on load...
>
> Where did you get your information from?
OK, Cyrille, what do you do when the engine starts to ping as you go up hill
with a lot of throttle? Most of us back off the advance a bit. The engine
can take a lot more advance (which allows for better gas mileage) under low
load conditions like cruising. The engine tells the distributor about these
part-throttle circumstances via the vacuum connection; manifold vacuum is
higher under part throttle than under wide open throttle, so vacuum advance
gives us more advance with higher vacuum. What it really does is to retard
the timing under load, but that is not the way most of us grew up thinking
about it.
David Lieb
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