CIS basic idle/mix ballparking advice

[jdbubb at verizon.net (Dan Bubb)]

I carefully read your post Cathy and although it may not have been super 
clear it was correct.
I wasn't really responding to Gordy either, I've just seen quite a few posts 
that seemed to cloud the whole issue of vacuum advance and mechanical 
advance, blah, blah, blah......So, as usual I thought I'd dump my <.02 ;^)
As far as your primary plate it's a good indication it's in the right place, 
but that doesn't mean it doesn't need to be closed down a little more to get 
your idle under control.
Dan

----- Original Message ----- 
From: "C Boyko" <roccit_53@scirocco.cs.uoguelph.ca>
To: "Dan Bubb" <jdbubb@verizon.net>
Cc: <ydrogs@gmail.com>; <Scirocco-l@scirocco.org>
Sent: Sunday, July 31, 2005 10:33 AM
Subject: Re: CIS basic idle/mix ballparking advice


> On 10:08:26 am 07/31/05 "Dan Bubb" <jdbubb@verizon.net> wrote:
>> Uhhh.....
>> The distributor should not get vacuum at idle.
>
>
> Oh, sorry, I wasn't clear on my post, there was no vaccuum at idle, and
> vaccuum when off idle (as per guage...). Sorry. Before there had been 
> none.
> At all. I'm gonna stop replying, obviously I don't write real
> clearly!..though it may not have been my post to which you are responding.
>
> But, does this indicate that my primary plate is in fact correctly 
> adjusted?
>
>
>
> And, with all that big thread about vaccuum diagrams, did anyone ever come
> up with a location for them? The old (MkI) Bentley has them, but for the
> newer cars (MkII), I don't see them. I'm sure these would be very helpful,
> especially if you are doing a swap. If none exist (they surely must)
> perhaps one of the more graphically skilled on the list could cook
> something up, certainly there are enough cars out there as examples...just
> a suggestion..
>
> Cathy
>
>
>
> 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
>>
>>
>>
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>
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