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The Great Idle Mixture Screw Debate rages on! (was: Snorkel boy)



Yes, technically speaking, it is a "fact" that the idle mixture screw
affects mixture at all RPMs.  But the real question is how much?  The real
issue is HOW MUCH does it affect mixture at higher RPMs?

When you crank the screw you raise the plunger (inside the fuel distributor)
by X amount.  You're creating an offset or bias with respect to the position
airflow plate.  At idle, the amount X is significant or large compared to
the amount of air the engine is consuming.  Under full throttle at 4K RPM,
the amount X is far less significant.  Therefore, you have to crank the SHIT
out of that idle screw to make any real difference at high RPM.

My basic point is that it's unwise to try to "fix" or mask what is likely a
problem with your DPR (Differential Pressure Regulator) by jacking around
with that idle mixture screw.  On CIS-E systems, the DPR is the device truly
responsible for controlling mixture at all RPMs.  If you have mixture
problems, either the DPR is funky or you have some other problem like
incorrect system pressure, faulty fuel distributor, vacuum leaks, bad
coolant temp sensor, bad electrical connections, etc.

Of course it's awfully hard to argue with: "Well I turned the screw and it
fixed all my problems and now my car runs great."  So, I'm probably wasting
my proverbial breath!

Bradley

>-----Original Message-----
>From: Chris DeLong [mailto:green536@hotmail.com]
>Sent: Thursday, September 21, 2000 10:34 PM
>To: Shannon Fenton; Bradley Peet; Kevin Collins
>Cc: Scirocco List
>Subject: Re: Snorkel boy
>
>
>Shannon is right and the rest of you are wrong. Fact.
>
>
>> Ughh....will someone back me up and explain to turbo boy peet that the
>> mixture screw in the fuel distributer does not just affect idle mixture!
>> Now the idle bypass screw on the TB only affects bypass air when the
>> throttle is closed....



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