See Figures 1 and 2
There is no charcoal canister for 1970-71 engines. It can be found on the front of the left fender on late 1971-74 trucks and at the rear of the engine compartment, on or near the firewall on 1975 and later trucks (if so equipped).
The canister functions to cycle the fuel vapor from the fuel tank and carburetor float chambers into the intake manifold and eventually into the cylinders for combustion. The activated charcoal element within the canister acts as a storage device for the fuel vapors at times when the engine operating conditions are not conducive to the efficient burning of the vapors.
The only required service for the canister inspection at the intervals specified in the Maintenance Chart at the end of this section. If the charcoal element is gummed up, the entire canister will require replacement. Disconnect the canister purge hoses, loosen the retaining bracket bolt(s) and lift out the canister. Installation is simply the reverse of the removal process.