Rusty, does doing this reduce the output of the compressor? IE. if you slow the pump speed in half, wouldn't it cut the cfm in half as well and take twice as long to fill up? .
It absolutely reduces CFM but it may not be a linear curve. If you look up some bare pumps, there is probably a chart. I've got one that has always been troublesome. It's a microV and has a tiny motor pulley with a 3450 motor. This means of course that the motor pulley must be much smaller than if it were a 1725 RPM.