After cleaning the domes a few months ago, while setting the carbs, before starting the engine, I noticed the pistons could be raised with very little finger pressure, and realized I hadn't put any oil in the dampers. Put what I thought was the right amount in each (kind of hard to see the level) but one went up easier. I put some more oil in that one, and it was harder to lift. A few drops more and it seemed to take the same pressure to lift as the other carb. 

 

So I got the idea that oil level, as well as viscosity, affects how the pistons rise in response to vacuum (in front of the throttle plates)

 

So, is that correct, or am I missing something ?  Also, is matching finger pressure an acceptable way to set relative damper oil level ?  Depending on the light, it can be hard to see if the oil level lines up with the grooves on the damper stalk.

oil level cannot exceed a certain point or it just overflows internally and gets burned. It's possible to have too little, but not too much. As long as your not really low, or you've overfilled and it hasn't had a chance to overflow and stabilize, oil quantity can't have much impact on performance.

The oil level should only affect the force required to lift the pistons if the jiggly bits on the end of the stalk are not fully submerged. Once you've got enough oil in the tubes such that the bits are fully submerged when the pistons are in the full down position, then adding more shouldn't have any effect.

(cue beavis voice:) uh... he said jiggly bits... huh-huh-huh...

Shut up Beavis.