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Old 03-29-2015, 09:37 AM   #1
Robert Kenney
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Default Holley 2300/41xx Idle Circuit Restoration

This is is an often overlooked area to clean on the 2 and 4 bbl Holley 2300 and 4150 carburetors.. The idle/pilot jet serves to provide metered fuel to the idle mixture screws and more importantly the low speed transition slots that are uncovered by the throttle plates at the initial application of throttle. I will cover the two most common idle jet location types. In both cases the jet size is the same but the placement is different.

Symptoms of a fouled idle circuit:
1) poor idle quality.
2) rough poor performance at fixed low throttle position.
3) severe flat spot upon application of slight throttle( mimics a bad accelerator pump). Usually rapid large throttle application will be fine but when you are trying to gently leave a stop sign not so fine.

Type 1 is where the jet can bee seen without any further disassembly of the metering block than removing it from the carburetor body. Photo of this type below.
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Type 2 has the jet under the outer most two 1/4 inch cup plug locations on the top of the metering block. These plugs must be carefully removed to gain access and clean the jets. Simply blasting with carb cleaner most of the time won't do.
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To remove the plugs drill a 1/8 hole in the plug just deep enough to break through the plug. Going deeper can damage the jet. Using a sheet metal screw that will bite good in one turn (#10) pull the plugs out with pliers.
On either type that has a fouled idle circuit, I recommend removing the plugs. The idle passage that feeds the jet san hold dirt that will plug the jet.

In both designs the jets are .032-.035 inch diameter. I use a small solid copper wire to clean them in combination with carb cleaner and working the wire in and out and turning.
These jets are brass and can be damaged or easily enlarged from trying to clean with a hard tool like a steel pick or wire.

Once cleaned reinstall new plugs with can be sourced through many performance automotive suppliers.

A few useful fuel flow schematics for reference.
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Robert Kenney

People preach " Don't over think life, just go where it takes you". But I can't help but think of the Wise Ancient Mariner who looks toward the horizon for any sign of storm clouds.

Last edited by Robert Kenney; 03-29-2015 at 11:42 AM..
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Old 12-03-2017, 08:47 PM   #2
overdrivesteve
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Default Re: Holley 2300/41xx Idle Circuit Restoration

Hi,
What about this idle circuit plug on the side of the metering block where most carbs have a mixture adjustment screw - should it be pulled too for effective idle circuit cleaning?
And how is the best way to do that?
Thanks.
.

.
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Old 12-04-2017, 06:50 PM   #3
Robert Kenney
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Default Re: Holley 2300/41xx Idle Circuit Restoration

I don’t recall that being a removable plug. I don’t have a metering block to look at. That is not a critical part of the idle/pilot circuit.
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People preach " Don't over think life, just go where it takes you". But I can't help but think of the Wise Ancient Mariner who looks toward the horizon for any sign of storm clouds.

Last edited by Robert Kenney; 12-04-2017 at 09:36 PM..
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