Final float level adjustments of a Demon carburetor on a street-driven application are simply made by setting the fuel level to the 1/4 distance of the viewing window while the engine is idling. To check float levels on carburetors without sight glasses, remove the float-level plug, and ensure the outpouring fuel doesn't create a fire hazard on a hot manifold. Fuel should barely trickle from the primary or front end of the carburetor and be slightly higher at the rear. When turned clockwise, the hexagon nut on the needle-and-seat assembly will adjust the float downward, and upward when turned counterclockwise. To adjust the needle-and-seat, loosen the screw in the middle of the assembly very slightly and retighten when adjustments are finalized. By changing the float levels, the amount of fuel in the bowl and the carburetor's ability to feed the main jets is altered. By increasing the height of the float levels, the engine's response is quickened. This is an adjustment that is frequently used to eradicate a lean stumble. By lowering the float levels, the activation of the main metering circuits is delayed and consequently causes a leaner mixture when coming off idle. For street applications, the latter condition is more economical. To prevent clogging of the air bleeds, use a quality air cleaner like those from Rush Performance Filters.
Trying to reuse carburetor gaskets is a sure way to create problems. Shown here is a standard BG rebuild kit (PN 190004) for a mechanical secondary carburetor. It contains everything necessary including gaskets, O-rings, needle-and-seat assemblies, accelerator pumps, and power valves. | 
The BG Master Rebuild Kit (PN 195003) is for carburetors with vacuum secondaries. A new secondary diaphragm and a selection of springs are included. | 
A common item replaced when rebuilding a carburetor is the accelerator pump. Faulty accelerator pumps will normally cause a serious stumble when the throttle is opened suddenly. |
Accelerator pumps are found on the bottom of the float bowls on Demon and Holley carburetors. There are adjustments that can be made on the actuating arm and cam. | 
Power valves are replaced during a rebuild; changing their staging vacuum can also be a valuable tuning aid. | 
This is the baseplate of a Demon four-barrel carburetor. The primary throttle plates are at the bottom of the photo; the secondaries are at the top. Some secondaries are mechanically operated, while others use vacuum. There may be idle circuits in the primary side only, or both. |
The positioning of the throttle plate relative to the transfer slot is vital. As the throttle plates open, the transfer slots are uncovered and provide the fuel for the initial surge of air entering the manifold. At idle, however, the transfer slots must not be uncovered more than shown. | | |