Almost every car or truck produced for the American public comes with Electronic Fuel Injection and an “electronic brain” that controls when and how much gas the engine will get. In fact, if you have EFI on your street machine you are often discouraged from tuning the fuel injection. Discouraged to the point that any attempt to do so not only voids your warranty, but the engine may quit altogether and require a factory authorized technician just to get the engine to start and run again! Despite that, a large number of serious race cars still have carburetors, and tuning them for maximum performance is a skill that any drag racer needs to have. So what follows is a primer for those who may have a carbureted drag or street car and may want to tune them up.  

Engines produce vacuum and over the past 120 years engineers have contrived ingenious ways to harness its power to the engine’s induction system. Through a labyrinth of small-bore drillings in the carburetor, the vacuum draws a potent mixture of air and fuel.

So formidable is the mixture, in fact, it empowers naturally aspirated full-bodied 500cu in race cars to speeds in excess of 213mph in a distance no greater than 1,320 feet!

Although its fumes ignite, gasoline won’t burn and produce energy in its liquid form. Instead it needs to be emulsified (mixed with air), atomized, (separated into fine particles) vaporized (transformed to a gaseous state) and compressed in order for it to produce energy. The carburetor takes responsibility for the emulsification and the atomization processes while the vaporization occurs in the induction tracts. In addition, the carburetor must meet the air-fuel ratio requirements of the engine.

In the following sequence of pictures and captions we identify some of the chief components of the modular carburetor, illustrate their functions, acquaint you with common problems that adversely affect them, and tell you how to resolve them.

Engine vacuum draws fuel from the float bowls through the main jets into the passages of the metering blocks. The air required to emulsify the fuel in the metering block passages is drawn through these tiny air bleeds