A fuel air mixer includes a fuel air mixing tube having an inlet, an outlet, and an inlet inner diameter. A collar is attached at the mixing tube inlet and includes a first cylindrical portion upstream of the mixing tube inlet, and a body portion encircling the mixing tube at the mixing tube inlet and forming a fuel reservoir around the mixing tube inlet. The first cylindrical portion is spaced from the mixing tube inlet to create a gap placing the fuel reservoir in fluid communication with the mixing tube inlet. The first cylindrical portion has an inner diameter that is smaller than the inlet inner diameter so air flowing through the first cylindrical portion and into the mixing tube inlet draws gaseous fuel from the fuel reservoir into the mixing tube through the gap.