Jim Smart
October 1, 2009

The 2100 carburetor consists of a main body and air horn, throttle plates and shaft, accelerator pump, and automatic choke assembly. Each throttle bore, or barrel, contains a main and booster venturi, main fuel discharge, accelerator pump discharge nozzle, and throttle plates to control air/fuel flow. Fuel comes from one bowl where fuel is regulated by a float and needle valve. As fuel is atomized and burned, the float drops, unseating the needle valve to allow fuel to flow into the bowl. Floats are made of either brass or synthetic foam. Main metering jets screwed into the body regulate flow to booster venturis during power mode. They have no effect on idle mixture. Idle mixture screws (needles) regulate air/fuel mixture when the throttles are closed.

The 2100's accelerator pump system works off a cam located on the throttle shaft. As throttles are opened, the cam moves a lever, which leans on the accelerator pump diaphragm, injecting fuel into the throttle bores. This eliminates hesitation, providing a seamless transition from idle to power. The accelerator pump chamber has a check valve (either rubber or a steel ball) which allows fuel flow in from the fuel bowl and out via throttle bore nozzles.

A 2100's choke system works much like the 1100. A thermostatic, bimetallic coil spring gets its heat from a hot exhaust manifold. Heat is drawn via intake manifold vacuum to a coil spring, which, as it warms, expands and pulls the choke open. A choke unloader helps pull the choke open via intake manifold vacuum to reduce cold start emissions. A fast idle cam incorporated into the choke bumps the idle higher during choke operation for faster warm up. There is a fast idle adjustment as well.

The 2100 two-barrel carburetor ultimately evolved into the 2150 with a more sophisticated choke unloader, which came along in the early 1970s. This carburetor was in production until the mid-1980s.

Holley Carburetors
It wasn't until the '67 model year that Mustang got its first factory-installed Holley carburetor. Yep, we know the '65-'66 Shelby Mustangs were fitted with a 715-cfm Holley 4160 with LeMans float bowls, however they were installed at Shelby American. Jon Enyeart tells us there are two basic types of Holley carburetors that apply to Mustangs-the 4150 and 4160. There is a third one you see from time to time-the 1850, based closely on the 4160-as a standard garden-variety 400-600-cfm Holley replacement carburetor. The 4160 has only a primary metering block whereas the 4150 has both primary and secondary metering blocks. The 4160 utilizes a secondary metering plate, which takes the place of a metering block. It can be replaced with a metering block to create a 4150.

The Holley 4150 was factory installed on a Mustang for the first time in 1967 atop the 390 High Performance. That same year, Shelby American would top the 428 with a pair of 4160s. The 4150 carburetor was fitted with "Cathedral" center-pivot fuel bowls. Those 4160 carburetors got side-pivot fuel bowls.

Holley carburetors are identified differently than Autolites. If it's an aftermarket Holley, it will have only a List number and Julian three-digit date code and year on the air horn. If it's a Ford/Holley carburetor, it will have both List and a Ford part number/date code on the air horn. If you've found a Shelby/Holley carburetor, you will see the List number and a three-digit date code without the Ford part number.