Emission controls in older carbureted engines relied on forcing additional air from pumps and valves located just before the exhaust manifold to ensure better burns. This is known as a secondary air injection system, and today has evolved to increase the efficiency of Catalytic Converters. Failed pumps and leaks are common signs of a bad Air Injection System, leading to off air and fuel ratios and poor acceleration. Remember to check the Manifold Gaskets and Seals for wear and tear when examining the exhaust.