PVT PLT OF A C170A MADE A PRECAUTIONARY LNDG AFTER NOTICING A DECREASE IN ENG RPM. CARB PROB IS SUSPECTED.

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WHILE ENRTE FROM ANNAPOLIS; MD; TO CAMDEN; SC; I BEGAN NOTICING A SLIGHT DECREASE IN RPM'S. IT WAS INTERMITTENT. BECAUSE I HAD FOUND SOME DIRT IN THE CARB SEVERAL MONTHS BEFORE; I TOLD FLT FOLLOWING I WOULD RETURN TO PETERSBURG FOR A PRECAUTIONARY LNDG. A MECH LISTENED TO THE ENG AND DRAINED FUEL BUT FOUND NOTHING WRONG. I ASKED WHAT HE WOULD DO AND HE SAID HE WOULD TEST FLY AND IF NOTHING OCCURRED; KEEP GOING. I DID THIS AND THE FLT CONTINUED UNEVENTFULLY FOR ANOTHER HR AND 50 MINS. NEARING ROCKINGHAM; NC; THE SAME THING HAPPENED AGAIN. THIS TIME I LANDED AGAIN AND LEFT THE ACFT PENDING REMOVAL OF THE CARB FOR INSPECTION; SINCE MORE DRAINED FUEL REVEALED NO WATER OR OTHER CONTAMINATION. ON OCCASION I HAVE NOT FULLY TIGHTENED THE THROTTLE LOCK AND NOTICED A SLOW DECREASE IN RPM'S BECAUSE VIBRATION WAS SLOWLY CLOSING THE THROTTLE. THIS PRODUCED MOMENTARY ANXIETY UNTIL I REALIZED WHAT I HAD NEGLECTED TO DO. LATER I WONDERED IF THIS IS WHAT HAD HAPPENED OVER PETERSBURG; BUT IN THE SECOND HALF OF THE FLT; I RECHKED THE THROTTLE LOCK SEVERAL TIMES. AT NO TIME DID I FEEL THERE WAS AN EMER SINCE I HAD SUFFICIENT FUEL; PLENTY OF ALT AND AN ARPT CLOSE AT HAND. I MADE IT CLR IN MY XMISSIONS TO FLT FOLLOWING THAT I WAS MAKING A PRECAUTIONARY LNDG AND THAT NO EMER EXISTED. HOWEVER; I SHOULD HAVE LISTENED TO MY OWN JUDGEMENT; AND NOT THE MECH WHO; AFTER ALL; WAS NOT THE RESPONSIBLE AUTH IN DECIDING TO CONTINUE THE FLT. EVEN AFTER MANY YRS AND MANY SOUND JUDGEMENTS; 'GET HOMEITIS' CAN STILL INFLUENCE EXPERIENCED PLTS AND IN THIS CASE I WOULD HAVE BEEN BETTER OFF BY REMAINING AT PTB AND GETTING THE CARB TORN APART INSTEAD OF CONTINUING ON WITH AN UNKNOWN PROB.