Soak the emitters in vinegar (acetic acid) or weak muriatic acid (swimming pool supply) overnight and it will dissolve the calcium carbonate that is the likely cause. Rinse and clean 'em up with an old toothbrush and thin wire. Flush system with the emitters out (just let it run after cleaning tank as best you can. Worked for me.
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)