I have some zones that are losing pressure. I find that when the timer opens them, the sprinklers will not pop all the way, but they will if I open the bleed screw.

I've found a couple sections of wire where the insulation has been stripped and there is some exposed wire that is corroded. Can this cause a reduction in the voltage getting to the solenoid? Can reduced power to the solenoid cause a reduction in pressure, or is a valve fully open or fully closed with nothing between?

I've solved this problem before by simply replacing the valve, but this is a good brass one, and I would rather try to fix the actual problem if possible.