Starting today, (and probably over several posts) I am going to describe 'ONE METHOD' of how to tune a Holley carburetor.
In the "old days' (when Holley Carburetor was being funded for "Calibration Development" by the Big OEMs: GM, Ford, and Chrysler), Holley had a specific process on how they dialed in their calibrations.
Holley had Horiba Air/Fuel Meter equipment even in the 60s and 70s but it was $$$$ for one set of equipment. It did allow on the road testing of the calibrations though.
http://www.horiba.com/automotive-tes...mexa-730-2592/ Today many Pontiac Enthusiasts have the same or better equipment.
So Step #1 is you start off with a Basic Holley Calibration. I have taken apart a very large sample of Holley Carbs over the years and "Finger-Printed" the calibrations as the standard for how that specific "List Number" carb was built.
So in Step #1 we put the Carb back to the specs that the "Holley Carburetor Calibrator" came up with in the first place.
The main parts of the Calibration are:
a) The Idle Jet (also called the Idle Feed Restriction IFR by many people today. I will use "IFR" in the future to describe that Calibration Orifice.
b) The Main Jet
c) The Idle Air Bleed
d) The High Speed Air Bleed.
e) The Main Well "Kill Bleed" (also called the Syphon Break).
f) The Idle Mixture Screws
(These parts are located in the Metering Block or in the Air Horn area above the Main Boosters.)
g) The Idle Transfer Slot is located in the Throttle Blade Base
h) The Idle Discharge Hole is also located in the Throttle Blade Base
You, typically, put the "base calibration" back into the carb, adjust the Idle Mixture Screws to 1.5 turns from lightly seated on 2-corner idle carbs or 3/4 turn from lightly seated on 4-corner idle carbs.
On the 4150 series Holley carbs you set the Transfer Slot Window to about .020" exposed below the Throttle Blade
If you have a "Idle-eze" circuit in the carb you open that up to allow the engine to idle above typical Idle RPM initially
If you do not have a "Idle-eze" circuit you open up the air gap on the Secondary Throttle Blade Stop slightly.
Hopefully BEFORE you started the Holley Carb Tuning, you verified that the Engine Initial Spark Timing was to specification and the parts were in good working order.
You KNOW that you have good Fuel Pressure to the carb (measured with a Proper Fuel Pressure gage) and hopefully set to 6 psi
Holley Calibrators love 6 psi fuel pressure settings, higher or lower, they are not so happy as excessive fuel pressure raises the fuel level in the fuel bowl, changes the fuel level in the Main Wells and Idle Wells, changes the point of "Start-up" of different fuel/air circuits, and simply confuses the heck out of things. The 6 psi fuel pressure setting was specified for a reason.
More on tuning later.
Tom V.