In 1977 the carbs on the KZ650 were changed from the pilot (blunt tipped) screw to the pointed tip Airscrew. For some time carbs were available with both types of pilot/airscrews.

If your carbs have both types here is a tip on tuning.

Turn the pilot screws (blunt tip) all the way in, then set the airscrews as normal carburetor adjust procedure. Default is 2 (+/-)  1/4 turns out

Frame numbers affected

1977 KZ650 B                                        KZ650B-024641 THROUGH KZ650B-026991

1978 KZ650 B                                        KZ650B-027901 THROUGH KZ650B-028701

1977 KZ650 C CUSTOM KZ650C       KZ650C-007751 THROUGH KZ650C-10000