Are you using the Rainbird brand rotory nozzle or are they Hunter?
Check out this video of an Irritrol rotory nozzle vs the Hunter. It starts at 1:44.
Rotory video
I just bought a bunch of the Irritrols. The verdict's still out if I like them better than the Rainbird.
I don't get a chance to use them much but they sure are handy when you need them.
What I do know is, the Hunter brand gave me nothing but headaches. They all turned at various speeds. Some were so slow I was questioning if they were broken or not. They didn't seem to cover well enough either.
I suppose if you installed pressure regulating sprinkler heads so each head had the same amount of operating pressure things might work better.
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As far as cleaning them I don't have a clue. Maybe soak them in warm vinegar for an hour to disolve any calcuim build up.