[Tom Vaught]

Thought I would post a little bit on Holley Carb Idle Systems and Idle Systems in general.

1) First you have the Basic 2-BBL Rochester Carb, the AFB 4-BBL carb, the Rocjester Q-Jet, and many other carbs that had a "Dual Idle Circuit" system built into the carb.
Basically one for each Carburetor Bore. Pretty standard stuff here.

2) Then about the early to mid 80s, Holley decided to offer up the "4-Corner Idle" carbs.
(At least that is what people thought at the time.) One mixture screw for each barrel.

3) Now people had been putting multiple carbs on intakes for many years. Pontiac being one of them with their Tri-Power set-up BUT THERE WAS, as many know, AN IDLE CIRCUIT ONLY ON THE CENTER CARB. The end carbs did not have any idle circuit capability.

4) At one time, you could mount as many as 6 carbs on an aftermarket Pontiac
intake manifold. Most times the mechanic/tuner turned off all of the idle circuits on the carbs except for the center carbs on the dual Tri-Power set-up.

Because this is a Holley Carb Thread and we have given some history on the "other" carbs, now it is time to talk a bit about the Holley "Tri-Power" (Chevy) and the Holley
(MOPAR) 6-PACK idle systems.

The Holley "Tri-Power" (Chevy) and the Holley (MOPAR) 6-PACK Carbs had the normal two idle systems on the center carbs, (one for each barrel).

But the Holley Carb Guys were smarter vs the old mutli-carb guys in that they realized some benefits with adding fuel from the End Carbs at idle and part throttle conditions.
So they designed the Throttle Bases (not the metering block) with a Idle Screw for each End Carb barrel. They could not use the normal metering blocks on the end carbs because there was a lack of room to fit the Center Hung Float Bowls on the carbs as well as Metering Blocks. The Mopar and Chevy Guys really liked the "Looks" of the three RACE BOWLS on the carbs.

So how to make the Chevy and Mopar Guys happy and still have a idle circuit on the end carbs?

Here are some pictures how the Holley Engineers did it.

1st Picture you see the complete system and the lack of metering blocks on the end carbs. (You see the main body and the float bowl).

2nd Picture you see the special base plates for the End Carbs (with the sealing plugs installed).

3rd Picture you see the plug removed from the carb throttle base and the fine mixture adjustment screw.

4th picture you see the three parts to the assembly. (TWO CORK GASKETS (same one used on the normal metering blocks)
and the Mixture Screw. So with this you could fine tune the idle mixture coming from the main body of the end carb.

So you actually had a "6 Circuit Idle System" on the engines years before the "4 corner idle system" was put on the 4 bbl Double Pumper carbs.

So the Chevy and Mopar Guys had their 6 circuit idle system, but no room to run the normal metering blocks on all three carbs unless you used the "Side Hung" Float Bowls.

But Pontiac Guys are more fortunate, you can run the normal metering blocks and Race Bowls on a Tri-Power Pontiac manifold because there is more room! 1966 Cast Iron Tri-Power with adaptors or (Aluminum Tri-Power Intake Manifold from PY) with adaptors, and you can have a carb set-up that resembles the last picture but with Holley Race Bowls.

Tom Vaught