What was found
CERTIFIED FLIGHT INSTRUCTOR AND STUDENT WERE PRACTICING STALLS WHEN, AFTER 3 OR 4 STALLS, THE YOKE JAMMED IN THE REAR POSITION AND THE AIRCRAFT WENT INTO A SPIN. AIRCRAFT LOST OVER 700 FEET OF ALTITUDE BEFORE CERTIFIED FLIGHT INSTRUCTOR WAS EVENTUALLY ABLE TO RECOVER AFTER FORCING THE YOKE FORWARD. CERTIFIED FLIGHT INSTRUCTOR IMMEDIATELY FLEW BACK TO KCPS. MECHANIC THAT RESPONDED FOUND THAT THE YOKE HAD COME INTO CONTACT AGAINST A COPPER OIL PRESSURE LINE WHICH SEVERELY LIMITED YOKE MOVEMENT. MECHANIC REROUTED COPPER OIL PRESSURE LINE. AIRCRAFT HAD RECENTLY RECEIVED AVIONICS UPGRADE INSTALLATION THAT INCLUDED A FLIGHT CONTROL FREEDOM OF MOVEMENT CHECK AFTER INSTALLATION. ALTHOUGH MECHANIC STATED THAT THE COPPER OIL PRESSURE LINE WAS NOT MOVED FOR CONVENIENCE OF THE AVIONICS INSTALLATION, THE LINE WAS INADVERTENTLY MALADJUSTED DURING THE INSTALLATION THAT EVENTUALLY LED TO THE FLIGHT CONTROL MALFUNCTION WHEN YOKE WAS PULLED TO THE EXTREME AFT POSITION.