Holley 4779 750 cfm Double Pumper

The 50cc accelerator pump arm may be adjusted too tight and it may be bottoming out the diaphragm on the spring causing it to coil bind. This can create a pressure peak from the fuel pressure pushing against the diaphragm when the throttle is slammed open rather than being absorbed by the spring because it is in bind. Because the fuel doesn't compress, it creates these peaks and will rupture the diaphragm. You need to make sure the accelerator pump linkage moves the arm to the diaphragm as soon as the throttle is moved, but that it is just at the point where it just takes up any clearance and nothing else. Loosen the spring-loaded bolt and nut until you have visible clearance and then adjust it till the clearance is eliminated. Do not preload the lever or it can cause the above problem.