Some units use a well jet in addition to the step-up rod jet. The well jet is located in the bottom of the bowl next to the step-up jet. Other models use an additional fuel feed called the “constant feed.” This is a metered bushing pressed into the casting and allows a calibrated amount of fuel to flow from the bowl into the well at all times.
During idle operation, or with the engine shut off (with hot engine on an extremely warm day), fuel sometimes boils in the fuel bowl and in the various passages of the carburetor. The air bleed to the high speed circuit also acts as an antipercolator passage to prevent vapor bubbles forcing liquid gasoline from the nozzle. The design of the RBS also places the fuel level in the high speed well far below the nozzle cross-over passage.