Introduced on California cars in 1970, and nationwide in 1971, this system reduces the amount of escaping gasoline vapors. Float bowl emissions are controlled by internal carburetor modifications. Redesigned bowl vents, reduced bowl capacity, heat shields, and improved intake manifold-to-carburetor insulation serve to reduce vapor loss into the atmosphere. The venting of fuel tank vapors into the air has been stopped. Fuel vapors are now directed through lines to a canister containing an activated charcoal filter. Unburned vapors are trapped here until the engine is started. When the engine is running, the canister is purged by air drawn in by manifold vacuum. The air and fuel vapors are directed into the engine to be burned.
Replace the canister filter every 12 months or 12,000 miles on 1971 models; on 1972 and later models, it is replaced every 24 months or 24,000 miles. If the fuel tank cap requires replacement, make sure that the new cap is the correct part for your car.