An accelerator pump cap (30, 70, 100, 150) for an accelerator pump assembly of a carburetor, such as a motorcycle or ATV carburetor, has a cap body (30, 70, 100, 150) with a base (38, 80) and a sidewall (56, 78, 104, 154) projecting from the base (38, 80) defining a fuel chamber (44, 102, 152) within the cap body (30, 70, 100, 150) beneath an open top. Preferably, one or more outlet ports (60, 72, 112, 160) extend through the sidewall (56, 78, 104, 154) closely-spaced to the open top of the cap body (30, 70, 100, 150) to ensure that any vapor or gas residing within the fuel chamber (44, 102, 152) is flushed out of the fuel chamber (44, 102, 152) through the outlet ports (60, 72, 112, 160) when the accelerator pump assembly is actuated to supply fuel to the carburetor. Accelerator pump assemblies and the use of a separate collector ring (90, 120, 140, 170) within an accelerator pump cap are also provided.