For what it's worth. It appears as if restrictions on the suction side have the same effect on current as a restriction on the pressure side. Best I could do was plumb a ball valve in the suction side and start restricting it and watching the current. If I restrict it too much the pump basket starts getting sucked dry so I avoided that. Adding just a little restriction indeed dropped the current. The jury rig I use is airtight. Verified that years ago when I first started using this old pump to circulate before de-winterizing the real equipment. I always have air in the suction side and I think what's going on is air is coming out of solution under the vacuum. I see this more with colder water which makes sense. I can only easily use 1.25" pipe so that's a slight restriction right off.
Pump is an old Jacuzzi 1 HP SF-1 240V configuration
Running dry -- 3.7A
Full flow (best possible) -- 5.0A
Slight restriction -- 4.6A and down from there.
Al
Attachment 662