CIS basic idle/mix ballparking advice

[jdbubb at verizon.net (Dan Bubb)]

Uhhh.....
The distributor should not get vacuum at idle. One of the ports on the TB is 
"ported" vacuum. The little pin hole through to the inside is on the 
atmosphere side of the primary plate. It doesn't see vacuum until the plate 
is opened some. That's why it's important that the primary throttle plate is 
adjusted correctly, so the distributor doesn't have vacuum at idle and cause 
incorrect ignition timing.
Just to run over this whole thing again. Your engine needs a certain amount 
of advance at wide open throttle. This amount starts out around 6-10 degrees 
and increases to 30-34 degrees in the 3000-3500 rpm range and stays fairly 
constant from there on up. This advance is accomplished by the mechanical 
advance which is strictly RPM dependant.
When your engine is in cruise mode, 3000-4000 RPM and light throttle, it is 
not pulling in a great amount of air and fuel. As a result the mixture burns 
more slowly. Due to this the engine needs more ignition advance. This is 
accomplished by the vacuum advance. High manifold vacuum more advance, low 
manifold vacuum (WOT) low vacuum advance.
The thing is the engine doesn't need the vacuum advance at idle or lower 
engine speeds and both the vacuum and mechanical advance are designed to 
provide the correct advance based on zero vacuum advance at idle.
The KS ignition emulates this basic control strategy with better control.
Dan

----- Original Message ----- 
From: "Gordy Stedman" <ydrogs@gmail.com>
To: "Dan Bubb" <jdbubb@verizon.net>; <Scirocco-l@scirocco.org>
Sent: Saturday, July 30, 2005 8:28 PM
Subject: Re: CIS basic idle/mix ballparking advice


If you have a vaccum advance distributor make sure the place you
attach the vaccum line to on the TB, usually before the butterfly
valve, is not plugged or clogged.  I finally found out the reason my
car was running so sh*#%y was because my distributor was not geting
any vaccume. I had 2 outlets on the back of the TB and just switched
the line to the one that weas sucking.  Just an experience I had that
someone else might run into.  Also, what Dan said on adjusting the
throttle isle position is right on, as always:)

On 7/30/05, Dan Bubb <jdbubb@verizon.net> wrote:
> I'd start by backing off the primary throttle plate stop screw. It's right
> on top with an 8mm locking nut and usually some yellow paint to hold it.
> Back that out until the plate is fully shut then screw it in just enough
> that you know the plate has been opened some. The plate will tend to bind 
> if
> it's allowed to close all the way and I believe that is the purpose of the
> stop screw, to hold it just a tad open. Alot of times people don't realize
> there is an idle adjustment screw and use the primary plate screw to 
> adjust
> idle, so maybe that's it..
> Also, make sure the secondary plate is closing all the way. Sometimes they
> will bind open just a bit.
> If those two aren't it, then it's either a vacuum leak, auxilliary air 
> valve
> that's not closing fully or an intake duct not fully seated.

-- 
Gordy
MK1 x 3
Audi 80 - Slated for parts car