My 773 is stalling after about 5 minutes of use. If I prime the fuel system I can get it to run for another 5 minutes. When I open the bleed screw on top of the fuel filter I can hear vacuum. I've replaced the fuel filter and it's not any better. I'd like to check the pickup tube in the tank but, I'm not sure where the tank is and how to get to it? Has anyone done this? Any advice would be apprecitated. Thanks.