I have a 1996 Volvo Penta 7.4 that will not stay running. It cuts off after a minute or so. It does need some priming to get it going. I started at the fuel pump relay and replaced that first. Next I replaced the fuel pump. Still same thing. Next I rebuilt the carb. Same thing. Lastly I cleaned and inspected the distributor. Same result. Not sure where to go next or what I am missing. Fuel lines seem to be fine. HELP!