Vacum leak or leaking shut off valve on the pump. I wouldnn't try the shut off as a DIY as I've seen people manage to get the pin on the wrong side of the lever and stick the engine wide open throttle. If you do test and attempt repair, retest shut off function with a hand pump PRIOR to starting it. (you'll watch the shutoff arm pull down as you activate the valve)
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.