Re: [AMC-List] Vaccuum advance

["John Elle" <johnelle@xxxxxxxxx>]

Date: Sunday, April 16, 2006 10:37 AM
From: steven.rideout@xxxxxxxx
 
Could somebody tell me how much additional advance shoud be added when
the vaccuum port is connected on a motorcraft electronic distributor 
when i connect mine my timing goes from 12 to 40 does this sound correct
 
Steve Rideout
Tottenham/Ontario
1973 fresh plum AMX
 
Steve
I do not have data on that particular distributor. The proper
distributor for your car has points so it is a later conversion. 
Using data which I find to be typical an additional 28 degrees advance
is a bit large for just hooking up the vacuum. But then again that
distributor is probably designed to use ported vacuum rather than intake
manifold vacuum. One of the differences would be that vacuum at idle
would be about zero (0) thus when hooked up would  not show much of an
increase at all depending on what your idle speed is at the time that
you measure it.  So my first guess is you are using intake manifold
vacuum for your vacuum source. 
 
In general, the distributor that probably came with your car would have
been set for 5 degrees advance at idle with a total of about 23 degrees
mechanical advance at somewhere around 3000 rpm plus an additional
maximum of 6-8 degrees available from the vacuum but once again it would
have been ported which depending on rpm can be significantly lower than
intake manifold vacuum. 
With the advent of smog requirements things got a bit tricky and in many
cases poorly controlled until computers became available.
Part of the data that you are looking for is probably printed in the
electrical and/or emissions control section of the TSM for the same year
that your distributor is.
John. 
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