A push button air primer including a priming piston slidably housed in a primer housing and a sealing piston slidably housed in the priming piston. To prime the carburetor, the operator depresses the priming piston causing both priming piston and sealing piston to slide within the primer housing until the sealing piston bears against the carburetor body to seal an opening to an internal vent passage. Further movement of the priming piston forces air from the housing into a fuel bowl, thereby pressurizing the fuel bowl and causing fuel to move from the fuel bowl into the throat of the carburetor.