Originally Posted by trimmer2
The treadle on a machine with a clutch motor is not a speed control.It just engages the clutch or disengages it.So its either going or not.You control the speed of the machine by slipping the clutch with your foot. You can slow the whole machine down by changing the pulley but then to go really slow you still have to slip the clutch.
The spring is there to adjust treadle tension. So by adjusting it you gain some control. It's easier for a newbie to ease into clutch engagement then to have a direct connect.
Sometimes it's worth trying to work with what you have before swapping parts. Well, that's my method anyway.