A primer assembly is provided for use on a carburetor that is vented through an external vent on the primer. In at least some embodiments, the assembly comprises a housing comprising an open end and an outlet with a flexible primer bulb inserted into and closing the open end of the housing, thereby defining a volume within the housing. There is a vent in the primer bulb. A carbon canister is positioned within the volume defined in the housing such that the vent and the outlet are in fluid communication via a flow path that extends through the canister. The carbon canister adsorbs fuel vapors from the carburetor. During normal operation of the engine, air enters through the primer vent and purges the carbon canister of the adsorbed fuel.