DURING AN INSTRUMENT CLIMB-OUT FROM TETERBORO AIRPORT, THE PILOT WAS ADVISED BY DEPARTURE CONTROL THAT HE WAS IN RADAR CONTACT, AND TO CLIMB & MAINTAIN 4000 FT. THE PILOT ACKNOWLEDGED THIS TRANSMISSION AT A RADAR RECORDED ALTITUDE OF 1800 FT MSL. THE FLIGHT WAS RECORDED REACHING AN ALTITUDE OF 2800 FT MSL BEFORE STARTING A DESCENT. NUMEROUS WITNESSES OBSERVED THE AIRPLANE DESCENDING OUT OF THE CLOUDS; ONE WITNESS DESCRIBED THE DESCENT AS A SPIN WITH NO FORWARD MOTION. ON-SCENE WRECKAGE EXAMINATION OF THE LEFT PROP SHOWED ONE BLADE BENT AFT APRX 120 DEG; OTHER BLADE STRAIGHT & NOT BENT. PROP WAS NOT IN FEATHERED POSITION. LEFT ENG TEARDOWN REVEALED 2 OF 6 FUEL INJECTOR NOZZLES RESTRICTED. LAST DOCUMENTED FUEL INJECTION SYSTEM CLEANING WAS IN 1985; BENDIX (MANUFACTURER) RECOMMENDS EVERY ANNUAL INSPECTION OR 100 HRS. THE AIRPLANE WAS 188 LBS OVER MAX GROSS WEIGHT; CG APRX 1 INCH AFT OF MAX AFT LIMIT. AFT CG INCREASES VMC AIRSPEED.