[DML] Re: Cold Idle Problem - one more thing (CIS)

["content22207" <brobertson@xxxxxxxxxxxx>]

I think CIS is rather misunderstood in the DeLo community. It serves
the same function and has exactly the same effect as cracking open the
throttle plates (except of course the ported vacuum barb remains
closed). That's all it does. CIS does have the advantage of *VARIABLY*
cracking the throttle plates, which is how idle speed remains constant.

Compare CIS to a carburetor. Cold, carb has a cam that pushes the
throttle plates further open (manifold vacuum actually increases, thus
fuel mixture enriches, because of the choke plate. K Jetronic
accomplishes the same thing via the CPR). Cam has multiple step downs
that incrementally allow the throttle plates to close to their warm
setting, cracked a certain distance by a set screw. Common practice is
to use a solenoid to push the throttle plates further open again when
accessories such as A/C are energized. 

For some reason many DeLo owners think that CIS is mandatory. Nonsense
-- CIS wasn't even introduced until 1981. K Jetronic PRV's had been in
production at least 5 years prior, idling off the brass manifold
screws (with a device called the "auxiliary air valve" to serve the
same function as cracking the throttle plates further open on a cold
engine). CIS is nice -- when properly functioning -- but hardly mandatory.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "joekuchan" <josephkuchan@xxxx> wrote:
> 
> 
> On a careful re-read of Bill's posting I think what he's saying is 
> that as long as the total restriction presented by the throttles, 
> idle speed motor, opened manifold screws, or what have you, is held 
> constant, then for a given air flow vacuum will be the same. In other 
> words, if the throttles are cracked open slightly AND the idle speed 
> motor is able to compensate by closing a bit, then the vacuum will 
> stay the same. This is true within the limits of the idle speed 
> system. 
> 
> What I wanted to be clear about was that vacuum is the result of two 
> things: air flow and a restriction. The restriction is required for 
> the vacuum to be present.
> 
> I neither wrote nor discovered the laws of physics, but that is just 
> how it is. That is why dashpots work, why carburetors work, why 
> turbos in suck-through designs are more prone to drawing oil through 
> the compressor seal when the air filter gets dirty, why free-flow 
> exhausts are "good", etc.
> 
> If what Bill is saying is that it doesn't matter what the restriction 
> is caused by, for an equal restriction at a given air flow the vacuum 
> will be the same, then I agree. I just wanted to be clear on how that 
> vacuum gets produced!
> 
> -Joe Kuchan
> 
> --- In dmcnews@xxxxxxxxxxxxxxx, "content22207" <brobertson@xxxx> 
> wrote:
> > 
> > 
> > The engine produces the same amount of vacuum whether it's idling 
> off
> > cracked throttle plates, opened manifold screws, or CIS. All three
> > accomplish the same thing.
> > 
> > One thing cracked throttle plates will do that neither CIS nor the
> > manifold screws will is open ported vacuum. On a stock DeLo setup 
> that
> > only affects charcoal canister purge.
> > 
> > Bill Robertson
> > #5939
> > 
> > >--- In dmcnews@xxxxxxxxxxxxxxx, "Joseph Kuchan" <josephkuchan@xxxx>
> > wrote:
> > > 
> > > You should start by readjusting the throttle to the proper 
> position.
> > You 
> > > will never fix it if you make "masking" adjustments, although I 
> know
> > you did 
> > > that just to get by with the intention of fixing it properly at 
> this
> > time. 
> > > By turning the throttle adjusting screw you almost certainly 
> reduced
> > the 
> > > amount of vacuum the engine produces. That can affect your 
> braking,
> > among 
> > > other things, so start by getting that set properly.
> > > 
> > > Next have a look at the idle speed motor and its controls.
> > >








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