1. Debris, especially small particles of foam breaking away from a fuel cell, frequently gets stuck in one of the carburetor's needle-and-seat valves, causing it to jam open.  Consequently, as the fuel pump works to maintain pressure in the line, the fuel bowl becomes flooded and excess fuel gushes up through the vent tube and down the venturi bores into the engine. The symptoms include an engine that is hard to start, that has an uneven idle, and that performs poorly. The cure is to remove the debris, replace the foam in the fuel cell, if necessary, ensuring it's compatible with the race fuel used, and to install a new fuel filter.

2. If debris succeeds in passing the needle-and-seat valves, it often gets stuck in a main jet or in an idle-feed restrictor. A blocked or partially blocked main jet would cause loss of flow in a boost venturi and the fault is therefore obvious (one booster displays poor or non-existent flow while the others perform normally). An idle feed restrictor is a tiny orifice of .029 to .040-inch, and is situated in the idle well of the carburetor's metering block. On less expensive street carburetors, this tiny orifice is drilled into the bottom of the idle well; on competition carburetors, a removable brass idle feed restrictor jet is threaded into a tapped hole at the top of the idle well, placing it nearer the idle air bleeds. Both idle-air and high-speed air bleeds are also vulnerable to blockage, causing a rich stumble or cough. The idle feed restrictors and main jets (located in the metering blocks) control fuel metering, while the eight, brass air bleeds (located in the top air-entry face of the carburetor) meter air. Clean these jets with carburetor cleaner and compressed air.

3. Four-barrel downdraft, standard flange carburetors have three fuel-metering circuits: idle, main and accelerator pump (all large-flange King Demon carburetors and some Holley Dominators have four circuits). Their functions are closely related. When the throttle plates open, the plastic cam mounted on the throttle shaft and the accelerator pump arm is activated. This pump arm with its spring-loaded adjusting screw must make contact with the smaller pump lever (a rocking arm) that attaches to the bottom of the fuel bowl. If the throttle plates open before the rocking arm is activated, the engine will receive a gulp of air without the necessary shot of fuel from the accelerator pump circuit. Further, to ensure the accelerator pump mechanism is not being forced beyond its mechanical limits, confirm that an additional travel of .010 to .015-inch is available at fully open throttle.

4. The rate of discharge from the accelerator pump circuits and also from the idle feed restrictors usually needs increasing to match any increase in plenum volume or camshaft specification. Introducing an open spacer, a larger intake manifold or bigger camshaft often requires additional pump shot, or larger idle-feed restrictors, or both.  Increasing the discharge from the accelerator pump is quickly accomplished by installing larger pump nozzles (squirters) or by altering the profile of the plastic cam on the end of the primary throttle shaft; increasing the size of the idle feed restrictors is a common cure for overcoming idling difficulties with a newly installed performance camshaft.

5. High-performance camshafts require increased initial ignition timing.  They create longer duration valve openings; consequently, generating less depression (signal) at the carburetor at idle.  As a result, the air-fuel droplets are larger, atomization is poorer, the burn rate is slower, and the combustion is incomplete. To overcome these induction changes, increase the value of the initial timing.  DR