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Re: [T3] Vacuum Advance and setting ignition timing


Thanks for the thorough help.  I printed out the post so I can look at the vacuum advance
(I have tested it before and it works) and the total advance over the weekend.

I was able to check where the vacuum hose to the dizzy is connected and it is attached at
the plenum/intake air distributor on the underside close to where the air cleaner elbow
attaches.  So it looks to me like its connected where the retard hose should go; however,
I don't know exactly where the Throttle Body is.  The Throttle Valve switch is also
connected to the plenum on the side so I need a little clarification for where the vacuum
adv. hose SHOULD be connected.  It the throttle body underneath the plenum?  And also,
where should the vacuum advance hose attatch.  Sorry for the basic question, but it'd be
great if a big part of the solution were as easy changing where the hose attaches.

thanks!

I looked through the Bentley for a diagram of the hoses but there weren't any. However,
it did say removing the vacuum retard hose while the car was running would move the
timing/advance 15-18mm which is pretty close to what my car does when I remove the vac.
hose.

>
> ... 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).

And excuse my ignorance, but where should it connect?  


--- Shad Laws <shad@lnengineering.com> wrote:
> Hello-
> 
> > 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

> 
> 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
> http://www.LNengineering.com
> 
> 
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