It was asked:
> How many degrees does the vacuum advance timing?
>
> What would happen if the timing was set to 0 or less
> degrees static and then hook the vacuum line to the
> manifold?
Repeat after me: no no no no no no no.....
That is NOT how the vacuum advance works.
Full WOT advance should be about 30 (maybe 35) degrees. More than
that and you get detonation and destroyed pistons. I believe a couple
other list members can attest to that?... :-)
So the idle (there's no mechanical advance at idle if the distributor is in
good order) should be: 30 degrees minus amount of mechanical
advance. A pre-smog distributor has 15 degrees advance (7.5 degrees
of CAMshaft advance=15 degrees at the CRANK). 30-15=15.
Hey - pretty close! An SU car should be set to 16 degrees BTDC and
a Solex at 18 degrees.
A smog distributor is 15 degrees cam, 30 degrees crank. 30-30=0.
Yup: smog cars get set 0 BTDC which is why off-the-line performance
sucks, errr, I mean, is poor. Give it a few degrees advance and it'll
run MUCH better. It'll also melt a piston pulling a hill :-(.
The vacuum advance affects the timing during PARTIAL throttle. At
WOT you have no vacuum advance, at idle you have no vacuum
advance. In the middle, you can advance past 30-35 degrees because,
well, that's just how an internal combustion engine works...
The vacuum line goes to the carburetor vacuum port. (On a smog
car, it routes thru a temperature switch. When the engine starts to
overheat, it adds advance. Different topic...). Any other routing is
incorrect.
BTW, Solex carbs do not use the vacuum line.
-- John
John F Sandhoff sandhoff@csus.edu Sacramento, CA
p.s. When you take apart the distributor, the advance plate will
have either a 7.5 or a 15 stamped on it. Now you know what that
number means!
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