RETURN LAND DUE TO 2 ROUGH RUNNING ENGS.

Narrative

I WAS FLYING A DC-3 ON AN AIRWAY; 40 W OF SAN JUAN. IFR FLT PLAN; BUT VFR CONDITIONS; WAS LEVEL AT 4000 FT. APPEARED TO HAVE A ROUGH RUNNING ENG AND DID A MAGNETO CHK IN THE AIR AND IDENT THE R ENG AS THE PROB. WASN'T A SERIOUS PROB AND BELIEVED I MIGHT BE ABLE TO COMPLETE THE FLT SAFELY. HOWEVER; ENG STARTED TO RUN ROUGHER AND AT THAT TIME THE OTHER ENG; WHICH WAS RUNNING NORMALLY UP TO THAT TIME; STARTED TO MISS BADLY. REDUCED PWR ON BOTH ENGS AND DID AN IMMEDIATE 180 TO RETURN DIRECTLY TO SAN JUAN. MAINTAINED 4000 FT. ADVISED ATC OF THE TURN BACK AND ATC DIRECTED ME TO A HDG OF 020 DEGS AND DSND TO 3000 FT. I ADVISED THEM THAT I HAD A PROB AND THAT I WAS UNABLE THEIR HDG AND ALT CHANGE. TOLD THEM IT WAS IMPERATIVE THAT I HOLD A DIRECT HDG BACK TO THE ARPT AND THAT I MAINTAIN MY ALT OF 4000 FT UNTIL I WAS CLOSE IN TO THE ARPT. I PROCEEDED STRAIGHT IN TO THE ARPT AND DSNDED TO PATTERN ALT CLOSE IN AND MADE A NORMAL LNDG. ON A NUMBER OF OCCASIONS; I WAS ASKED BY ATC TO CHANGE HDGS/ALTS; BUT WASN'T ABLE TO COMPLY. DID NOT DECLARE AN EMER AT THAT TIME BECAUSE THE ENGS SEEMED TO RUN SATISFACTORILY AT REDUCED PWR -- THE ACFT CARRIED NO CARGO ON THAT FLT. HOWEVER; CRASH FIRE WAS PRESENT ON TOUCHDOWN AND ESCORTED THE ACFT BACK TO PARTING -- WAS TOLD LATER THAT MY RADAR BLIP MERGED ON THE RADAR SCREEN WITH ANOTHER'S BLIP; BUT ATC NEVER ADVISED ME THAT WE WERE IN CLOSE PROX WITH ANOTHER ACFT. I WAS CRITICIZED FOR NOT DECLARING AN EMER AND THAT'S CONSTRUCTIVE AND BELIEVE I WILL FROM NOW ON. AS FOR THE ACFT WITH MALFUNCTIONING ENGS. I BELIEVE THE FAA SHOULD MONITOR ALL AVIATION OPS IN PUERTO RICO MUCH MORE CLOSELY TO ENSURE GOOD MAINT IS BEING PERFORMED.