Our Tillotson High Volume Pump Stack(Double Stack) section makes it easier to find the exact kit you need by separating the single and double stack kits. The high volume kits have fewer variations in components compared to the single stack kits. The main difference is the pump diaphragm material, the inlet need and fulcrum arm type, and the carburetor flange gaskets. Read the parts description for the best-suited carburetor kit.