Re: speaking of jets

["Tom Harais" <tjhemh@domain.elided>]

Terry:

If both mixture screws have no effect on idle quality, then I wouldn't
assume it's leaking fuel internally. Instead, I'd check two other
probabilities. I'll bet he isn't running on the idle circuit at idle for
one of two reasons.

As you might remember, Holley's (and others) have "holes" or slots inside
the two primary venturies towards the front for fuel to enter during idle.
When the throttles are almost closed, these holes or slots are below the
throttle plates and subject to manifold vacuum. The idle fuel flows out and
mixes with the air coming around the very slightly opened throttle plates
and the engine idles. But, as soon as you just crack the throttle plates
open a hair, these idle slots are above the throttle plate, no longer
subject to engine vacuum and should stop feeding any fuel. At that point,
the air flow in the venturies is sufficient to begin drawing fuel through
the jets, which are located above the throttle plates, usually with little
venturi boosters of their own, and the engine is running on the main
circuit and idle is out.

I'd check the throttle opening at idle. Chances are the throttle is too far
open so the idle circuit is out of the picture and hence, making mixture
adjustments has no effect. 

Or, there is something wrong in the idle circuit so it doesn't work at all 
In that case, he was "forced" to set the idle speed screw such that the
throttle plates are past the idle circuit and he is running on the main
circuit.

In either case, changing idle mixture will have no effect on the engines
running.

Tom H.