Question
My zone 1 out of 6 has little pressure and the pump cycles on and off at 2-4 second intervals on this zone.  All other zones work fine.  I found the zone and turned the big knob fully open and it was almost OK.  There a small knob on top of the large one (Toro) that I turned to maximize the flow, but when the system cycles to Zone 2, Zone 1 wounldn't shut full off.  I had to shut the little knob and it messed up the flow of the zone somewhat.  Why would this tweaking be necessary if all was fine last week.

Answer
The valve works with the bleed screw (thats the little one on the top) because you are allowing the control water to escape. The reason it won't shut off when the next valve come on, it need that water to close it's self. Enough tech stuff.
The valve need to be cleaned internally or replace. Something has contaminated the internal parts of the valve it just can't function the was it needs.

Thanks for your question.

Matt