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Re: [T3] Vacuum Advance and setting ignition timing


> I have a quick question.  I have read that you can set the ignition timing
with the
> vacuum advance hoses plugged OR unplugged (left connected).

It's true that for a dual advance (centrifugal and vacuum) distributor with
no vacuum retard the vacuum advance shouldn't play a role in idle timing.

> When I disconnect and plug the vacuum hoses, the idle drops ~200 RPM and
the timing
> retard ~10-15 degrees.

Something is fishy!

Let's try starting over from the start:
First, disconnect all the vacuum lines (plug them at the intake end, but
leave the distributor end open to the atmosphere).  Then, rev the engine to
at least 4000rpm and set timing to 28 degrees advanced (some stock dizzies
took 3800rpm to hit max advance, so at least 4000rpm is necessary to cover
all bases).  This can be measured by using an advancing timing light or by
putting another notch on the T3 aluminum outer fan piece (I haven't done
this on a T3 in awhile, but there 18, 36, or 72 knobs on that piece so
counting degrees is easy).  Then, you should verify that the centrifugal
part of the advancing mechanism is working.  First, is the timing consistent
or does it jump?  Second, when you drop to idle, what is the timing then?
If it drops to 6-10 degrees or so, then all is well.

Then, test the vacuum advance diaphragm.  If you have a single vac canister,
then the nipple to use is the only one on the dizzy.  Put a hose on it and
suck hard while watching timing.  You should be able to make the timing
move.  If not, it's shot: do not hook it back up to the intake system or
else you'll have a permanent leak.  If good, hook it up.  The other end of
the hose goes on the throttle body (NOT on the plenum... the vacuum retard
goes there... I have a hunch that this may be one of your problems).

Since you don't have vacuum retard, just make sure that the nipple on the
intake that used to go to that part of the system is plugged.

Take care,
Shad Laws
LN Engineering - Aircooled Precision Performance

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