Depends on a couple of factors. North American cars changed from carb
vacuum to manifold in 71. If you have carb vacuum then a non-operational,
or a leaking, vacuum advance will have no effect at idle, you will only
experience loss of mpg when cruising. But if it is manifold vacuum then
loss of vacuum advance at idle from a seized points plate will result in a
lower idle, which quite likely will result in engine shaking. If the
problem is a split vacuum capsule diaphragm then as well as loss of advance
at idle you will get a weak mixture which will add to the problem. If you
suck and suck on the tube to the distributor, and as well as the points
plate not moving you can't draw any air through, then something is seized.
If you can draw air through there is a leak in the vacuum line, which
usually is the diaphragm, but could also be a split rubber coupling between
plastic line and capsule, if that is what you have.
PaulH.
----- Original Message -----
> I did find that the vacuum advance on the distributor is not working. I
> always
> check this at tune-ups by sucking on the hose that goes to the inlet
> manifold.
> Normally, this makes the points plate rotate. Now, it is doing nothing.
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