• To ALL forum users - As of late I have been getting quite a few private messages with questions about build ups here on the forum, or tech questions about your personal project. While I appreciate the interest, sending me a private message about these topics distracts from, and undermines the purpose of having a forum here. During the day I wear many hats as a small business owner-operator and I work tirelessly to provide the absolute best service possible to you, our valued customer. When I created this forum I rounded up some of the best minds I knew so that any tech question you might have could be asked and answered by either myself or one of my highly experienced moderators, this way the next time this same question is asked the answer can be easily found and utilized by the next IH enthusiast having the same question. This allows me the freedom to run the day to day operations of the business and minimize the impact to shipments and shop activities that these distractions can cause. It is of the up most importance for me to complete the daily tasks in order to best take care of you our customer, all the while providing you a forum to get the level advice and input you have come to expect and deserve from the premier IH shop in the country.

    So with that I ask that anyone with a question about one of our build ups or a general tech question to please use the forum as it was intended. I am absolutely available by telephone to answer your questions as well but at times may direct you back to our website to better field your question or questions. Most other private messages I will be glad to answer for you.

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    Jeff Ismail

Holley 2300/41xx Idle Circuit Restoration

Robert Kenney

Super Moderator
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.

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.

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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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?


Robert Kenney

Super Moderator
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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