The modern "square" design of Holley carburetors was popularly introduced during the late 1950s. Because this style of Holley carburetor featured a simple, modular design with interchangeable parts and a great degree of adjustability, it immediately found favor with performance enthusiasts. In this story, we'll use the Holley 4150-series carburetors to illustrate how to select,

assemble, adjust and diagnose most Holley carburetors for non-emissions performance and restoration applications.
See Photo l.

Before we start, it's important to know that Holley carburetor "list" or identification numbers are found on the front of the choke tower or immediately behind the throttle linkage on racing carburetors manufactured with no choke towers. Keep in mind that the model number (4150, 4160, etc.) designates the carburetor configuration while the list number designates the actual design application.

Basic Metering Circuits
A Holley carburetor is made with four basic parts, the throttle plate, main body, metering block and float bowl assemblies. As with most domestically produced carburetors, a 4150 Holley has a choke, float, idle, off-idle, accelerator pump, air bleed, main metering and power-enrichment metering circuits.

Whether thermostatically or manually activated, the choke provides mixture enrichment for cold starting and cold driveability performance. Unlike many domestic carburetors, the 4150 Holley float...