SU with no spring for the piston?

I have rebuilt an H1 carb for my Morris 8. I think this carb originally came off a sprite but don't know for sure. I did not find a spring under the dome to return the piston to the down position. This was a set of two carbs, so I checked the other one and it too did not have a spring. I have a SU Haynes book and there is a reference to a weighted piston vs one that has a spring. These pistons do have a large steel ring and are heavier than most. My guess is that these carbs were from the 50s.
Any idea why no spring?
I was trying to use the lifting pin to test for fuel mixture and there was no change at all. I checked the carb with the dome off and it does lift the piston when the engine is stopped, but when running, the piston seems to be too high so no movement is felt. I can only run the car for a few minutes as the radiator is out to repair a leak. So I attached the top hose to the bottom hose after filling the engine and hoses with about a gallon of water. Maybe once the radiator gets back, I can make more progress on the adjustments.
Jerry

Weighted piston would indicate no spring, but unless the engine is up to running temp and idle is around 750~900 RPM the pin likely won't play into the equation. Get the rad installed and go from there.