Originally Posted by Frankie

Correct-o-mundo. When you open the throttle, you're opening either the butterflies in the venturi(s) of the carburetor or the butterfly(s) in the throttle body of your intake runner. All that really does is let more air in, changing the vaccum pressure of the motor. On a carburetor, the accelerator pump compensates for this momentary lack of fuel (due to the influx of straight air) by using a plunger and shooting gas kinda like a super soaker. In fuel injectiong the MAP/MAF sensor tells the computer to shoot more fuel. Once the vacuum pressure evens out, the caburetor will feed gas normally through its jets. On fuel injection, the computer controls the fuel delivery.

Basically, remember these two things: When you hit the gas pedal, you're really only delivering air, and a carburetor is just a controlled fuel leak.