Re: [ihc] RE: Circuitous idling

[bearbvd@xxxxxxxxxxxxxx (Greg Hermann)]

At 11:20 AM 5/10/04, Jim Grammer wrote:
>>Date: Mon, 10 May 2004 10:17:27 -0700
>>From: Joel M Brodsky <jmbrodsky@domain.elided>
>>Subject: [ihc] Scott Machalk and his high rev
>
>>There is an ongoing debate with the
>>mechanics of/in history about whether or not these screws control fuel or
>>air.  Everything I've read says that these are called Idle Air Bleed
>>Adjustments, so why does the truck quit when you turn them in?
>
>Depends on the carb design. In our Holleys of interest, the idle screw
>meters the flow of fuel into the idle discharge passage(s) in most cases.
>Examples are the 2300, 2210, 1904, 1910, and most of the 4xxx series 4bbl's
>IIRC. A noteable exception is the 4160 circa '73, which meters air into an
>idle emulsion setup. I have strong suspicions that this was emissions
>related and intended to limit the idle mixture adjustment range.
>
>Jim

On most Holleys, the idle mixture screws meter a fuel /air emulsion into
the idle discharge port--and the fuel part of that emulsion is drawn
through a (fixed size) idle 'jet' in the metering block after it has passed
through the main jet into the main jet well in the metering block. Screwing
the screw IN makes the idle leaner.

Note that the transition slots are also fed from the idle circuit upstream
of the idle mixture screws.

There are SOME Holley metering blocks, all emissions applications ASFAIK,
on which turning the dile mixture screws OUT gives leaner, and all the way
in is as rich as it will get the idle. Clearly an anti-tamper thing, and I
never bothered to figure out the passageway circuitry involved. These style
metering blocks came on most of the usual suspect 2 and 4 barrel Holleys in
SOME list #'s. Replacing them out with the other style metering blocks is
one alternative, removing the appropriate plugs and using a small number
drill on the idle jet is another---.

Greg