What was found
(CAN) LT ENGINE OF AIRCRAFT STARTED TO BACK FIRE AND DEVELOP LOW POWER DURING POWER REDUCTION AFTER TAKEOFF. PILOT'S ELECTED TO 'CAGE' ENGINE AND RETURN TO THE DEPARTURE AIRPORT. DIAGNOSIS FOUND A CARBURETOR THAT DID NOT FUNCTION CORRECTLY FORMED RANGE POWER SETTINGS, ALTHOUGH IDLE AND FULL POWER WERE FINE. CARB REPLACED WITH OVERHAULED EXCHANGE UNIT AND PROBLEMS WERE RESOLVED. DURING CARB EXCHANGE, SIGNIFICANT LEVELS OF CORROSION PRODUCTS WERE FOUND FLOATING OUT OF FITTINGS ETC.