DURING THE TAKEOFF ROLL, THE PLT WAS ADVISED BY TOWER THAT HE WAS TRAILING SMOKE. HE DISREGARDED THE RPT AS HE HAD SEEN SMOKE BEFORE AND THOUGHT IT WAS A NORMAL CONDITION. HE CONTINUED THE TAKEOFF. SHORTLY THEREAFTER, THE ACFT EXPERIENCED A THRUST LOSS OF THE RT ENG. AN ATTEMPT WAS MADE TO RETURN TO THE ARPT, BUT IT WAS UNSUCCESSFUL. THERE WAS EVIDENCE OF SINGLE ENG PERFORMANCE DEGRADATION DUE TO A 9.4% OVER GROSS CONDITION AND THE PLT'S FAILURE TO RAISE THE GEAR AND FEATHER THE RT PROP. THE PLT EXECUTED A FORCED LANDING INTO A VACANT LOT. INVESTIGATION REVEALED THAT THE THRUST LOSS WAS A RESULT OF THE FAILURE, DUE TO CHAFFING, OF THE RT UNFEATHERING ACCUMULATOR HOSE WHICH HAD BEEN MISROUTED DURING ENG INSTALLATION. THE ORIGINAL SMOKE OBSERVED BY THE PLT WAS DUE TO CRACKS IN THE RT EXHAUST SYS WHICH ORIGINATED FROM PREVIOUS WELD REPAIRS DURING ENG INSTALLATION. NEITHER CONDITION HAD BEEN IDENTIFIED BY OPERATOR MAINTENANCE PERSONNEL.