A LANCAIR 4P IN CRUISE AT FL240 HAS AUTOPLT INDUCE PITCH OSCILLATIONS. ON DSNDING; AUTOPLT EXCEEDED 2500 FPM. DISCONNECTED AUTOPLT.

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THIS IS AN EXPERIMENTAL LANCAIR 4P TURBINE PWRED ACFT. THE ACFT WAS BUILT AND TEST FLOWN BY MYSELF. ALL TESTING THROUGHOUT THE 40 HRS WAS DONE AT 17500 FT AND BELOW. I FILED AN IFR FLT PLAN TO ZZZ1 ENRTE TO ZZZ AT FL240. REACHING FL240; I FOUND THAT THE AUTOPLT WAS VERY SENSITIVE ON PITCH. AS FUEL WAS BURNING OFF; I HAD TO EVERY NOW AND THEN DISCONNECT THE AUTOPLT AND RETRIM THE ELEVATOR TO STOP PITCH OSCILLATIONS. ABOUT 150 NM FROM DEST; I WAS CLRED DOWN TO FL220. ON SELECTING THE AUTOPLT TO 1000 FPM DSCNT; IT EXCEEDED 2500 FPM; MY FIRST REACTION WAS TO TRIM THE ELEVATOR UP. THIS REDUCED THE RATE OF DSCNT. WITH NO WARNING; THE ELEVATOR PITCHED UP SHARPLY. IMMEDIATELY DISENGAGED AND PUSHED THE ELEVATOR FORWARD TO STOP THE CLB. AT 305 KTS IT CLBED THROUGH FL230 BEFORE I COULD RESUME NORMAL FLT. I DID NOT EXCEED FL240. THE REST OF THE FLT WAS NORMAL WITH THE AUTOPLT DISCONNECTED. THE RETURN FLT FROM ZZZ WAS DONE VFR AT 17500 FT. AFTER INSPECTION; IT WAS FOUND THAT THE SERVO FITTED MUST BE CHANGED TO A HIGH TORQUE SERVO. FURTHERMORE; THE ATTACHMENT POINT WHICH IS LOCATED ON THE ELEVATOR PUSH ROD MUST BE MOVED TO THE BELL CRANK TO STOP FLEX. THIS ACTION WILL BE TAKEN BEFORE ANY FLTS ARE RESUMED.