I suspect ignition is weak, the fuel well on the qjet are substantial. Fuel starvation generally produces a stumble, cough, then die. When that happens, restart would be difficult due to well being empty. I'd suggest monitoring the DC input to the HEI, if ok, likely the coil or driver. They make a kit with everything for the HEI for under $100. Cleaning the tank, and replacing fuel lines is never a bad idea, especially in boats.