33 CFR § 183.526 - Carburetors.
(b) Each carburetor must not leak more than five cubic centimeters of fuel in 30 seconds when:
(1) The float valve is open;
(2) The carburetor is at half throttle; and
(3) The engine is cranked without starting; or
(4) The fuel pump is delivering the maximum pressure specified by its manufacturer.
(c) Each updraft and horizontal draft carburetor must have a device that:
(1) Collects and holds fuel that flows out of the carburetor venturi section toward the air intake;
(2) Prevents collected fuel from being carried out of the carburetor assembly by the shock wave of a backfire or by reverse air flow; and
(3) Returns collected fuel to the engine induction system after the engine starts,