Abstract: A secondary air supply system, for an internal combustion engine having a closed crankcase includes a diaphragm air pump. The pumping chamber has one way valves such that ambient air may enter the pumping chamber only through the inlet port and exit the pumping chamber only through the outlet port to supply secondary air to the exhaust system. The actuating chamber of the diaphragm air pump is in airflow communication with the engine crankcase. The diaphragm air pump has a biasing means, either integral to the diaphragm or by a spring which acts on the diaphragm. The biasing means is calibrated to minimize the intensity differential between the positive and negative crankcase pressure pulses.

Abstract: An improved and easily adaptable system to provide secondary air for an internal combustion engine, including a single-cylinder engine unit having (i) a closed crankcase capable of experiencing pressure pulsations produced by the reciprocating motion of a piston in a cylinder, (ii) in the case of a four-cycle engine, a crankcase breather system including a breather assembly attached to a chamber integrally formed with the engine block, or, in the case of a two-cycle engine, an intake reed plate attached to the intake port of the engine, and (iii) an exhaust system including a catalytic converter. The secondary air supply system consists of an external secondary air pump, such as a diaphragm pump, as disclosed in U.S. Pat. No.