Thread: Carb question

Tweet

Originally Posted by ceh383

The bog you mention, what's the cause?

A carburetor works off Bernoulli's Principle. Airflow velocity is increased at the venturi(s) because they are smaller than the carb inlet at the airhorn. This increase of velocity creates a vacuum that pulls fuel from the reservoir bowl to mix with the incoming air. If there is not enough air flow (thus insufficient vacuum) to pull fuel and atomize it properly, then you will experience a bog. That's what happens when all four barrels open at low rpm's. Too much carburetor or too little motor, however you want to look at it.

Most carburetor manufacturers will recommend a vacuum secondary carb if you are using a converter that stalls at less than 3000 rpm's. Over 3000, there's enough airflow to support all four barrels and get a good mix, assuming you have sized the carburetor properly for the size of the motor. For max power street and strip, a good rule of thumb is cubic inches times 2 = CFM.