Constant running (if you have fuel and no leaks) is usually caused by a tear in the diaphragm or one of the check valves which is then intermittently stuck open as you say.
The check valves in a S.U. fuel pump are made made from thin plastic. When they tear the fuel pump will run as described, as the valves become stuck and then un-stuck periodically, causing major frustration. In an emergency the torn plastic cross check valves can be replaced with a triangle-shaped piece of thin stainless steel shim stock (inserting it into the valve body) This can work well and
Constant running (if you have fuel and no leaks) could be caused by a tear in the diaphragm or one of the check valves which is then intermittently stuck open as you say.
The check valves in a S.U. fuel pump are made made from thin plastic. When they tear the fuel pump will run as described, as the valves become stuck and then un-stuck periodically, causing major frustration. In an emergency the torn plastic check valves can be replaced with a triangle-shaped piece of thin stainless steel shim stock (inserted into the valve body) This can work well and get you home, but Joe Curto has replacement check valves.
Joe can overnight them to you, or you could simply take a few hours and replace the pump?