[Tom Vaught]

Tonight, I am going to talk a bit more about the Holley carb drillings and circuits of the typical 4150 Double Pumper Carb, specifically the Main Body with a "close up" picture. If you click on the image it will be much easier to see the different passages and their hole markings.

1) Because the Choke Mechanism is located on the left side of the picture there are two clues to which end of the Holley Carb we are looking at Primary? or Secondary?

There is also the Carb "List Number" 4779-9 showing on the Choke Tower so we know that the Carb is revision #9 of the Holley 4779 (750 cfm)
Double Pumper Carbs.

2) The Holes in the Main Body "face" are labeled "A", "B", "D", "E", "F", "G", "H", and "I" on the picture.

"A" is the drilling that goes to the Idle Air Bleed inside the air horn of the carb
"B" is the Accelerator Pump drilling that supplies fuel to the "Accelerator Pump Squirter"
"C" is not shown on the picture but should be a vertical drilling below the Letter "F" that supplies a
Vacuum Signal to the Power Valve Chamber "F"
"D" is the drilling that goes to the High Speed Air Bleed inside the air horn of the carb
"E" is the Main Well Passage that supplies fuel and air mixture (from the Emulsion Jets and the Main Jet)
to the Carb Booster) inside the air horn of the carb
I have mentioned "F" previously
"G" is the drilling for the Ported Vacuum Signal to the Distributor
"H" is the Air and Fuel feed passage to the Idle Mixture Screw
"I" is the discharge passage from the idle mixture screw which then goes downward to the Throttle Base Plate

There are two "Dimples in the Main Body gasket surface. Those holes have cast pins that fit into them and
hold the Holley gaskets in the right location on the Main Body surface.

On the outside perimeter are 4 threaded holes that the Bowl Screws thread into that hold the Fuel Bowl,
the Fuel Bowl Gasket, the Metering Block, the Metering Block Gasket securely against the machined Carb
Main Body surface.

So that is a short description of the Drillings on the Carb Main Body.
Have a nice evening.

Tom V.