DRG A LNDG GO-AROUND, THE ENG BGN RUNNING ROUGH, THEN LOST PWR. AN ATTEMPT WAS MADE TO MAKE AN EMERG LNDG ON A ROAD ADJACENT TO THE ARPT, BUT THE ACFT HIT A FENCE & AN EMBANKMENT BEFORE REACHING IT. AN INV REVEALED THE LOSS OF POWER WAS DUE TO A MALFUNCTION OF THE ENG'S MARVEL-SCHEBLER MODEL HA-6 CARBURETOR (CARB). EXCESSIVE WEAR OF THE SHAFT RETAINING SCREW ALLOWED MISPOSITIONING OF THE CARB'S ROTARY MIXTURE CONTROL (PN 242-541) AND BLOCKAGE OF FUEL FLOW. IN SEP 78, MARVEL-SCHEBLER/TILLOTSON (ORIGINAL MANUFACTURER OF THE CARB) ISSUED SVC BULLETIN (SB) #A1-78, BUT IT HAD NOT BEEN ACCOMPLISHED. THE SB PROVIDES FOR INSTLN OF A SPRING RETAINER (PN 55-A239) TO COUNTERACT END-PLAY WEAR ON THE MIXTURE CONTROL ASSEMBLY & RETAINING SCREW DUE TO VIBRATION. THE SPRING RETAINER ALSO SERVES AS AN ADNL MEANS OF RETAINING THE ROTARY MIXTURE CONTROL, EVEN IF THE EXISTING SHAFT RETAINING SCREW IS WORN OR BKN. THE ENG HAD A TOTAL FLT TIME OF 1065 HRS & 27 HRS SINCE THE LAST INSPN.