As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 1 ENGINE OSCILLATES DURING POWER TRANSITION AT APPROX. 80 PERCENT TORQUE. FOUND GOVERNOR WAS HANGING. FOUND INTERIOR OF UNIT VERY DIRTY WHICH CAUSED THE FLYWEIGHTS TO STICK. CLEANED FLYWEIGHTS AND REPLACED FLYWEIGHT PINS DUE TO WEAR. UNIT TESTED OK.