ACFT ON TEST FLT HAS FUEL PRESSURE DROP. ENG SHUTDOWN. ON LNDG ROLL OUT SMOKE FROM UNDER COWLING.

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ACFT WAS GIVEN A THOROUGH PREFLT AFTER MAINT WORK (SOME CYLINDERS CHANGED AND OIL LEAKS REPAIRED). ENGS STARTED NORMAL AND A 10-15 MIN GND RUN PERFORMED. EVERYTHING CHKED OUT OK. TKOF NORMAL AND CLB OUT NORMAL UNTIL PASSING THROUGH 4500 FT; WHEN I NOTICED ABOUT A 5 POUND DROP IN FUEL PRESSURE AND DROPPING SLOWLY. TURNED ON BOOST PUMP AND NO CHANGE AND PRESSURE STILL DROPPING; SO I SHUT OFF FUEL TO ENG FROM TANK (FIREWALL SHUTOFF) AND FEATHERED ENG AND RETURNED TO ARPT. ON ROLLOUT NOTICED SMOKE COMING FROM R HAND COWLING. GND PERSONNEL REMOVED COWLING AND EXTINGUISHED FIRE IN REAR OF ENG COMPARTMENT. THIS ACFT IS AN SMT; WAS ON PART 135 MAINT UP TO 2-3 WKS PRIOR WHEN IT WAS PURCHASED BY PRESENT OWNER. THIS WAS THE FIRST FLT AFTER BEING FLOWN FROM TOPEKA; KS; TO MENA; AR; WITH NO PROBLEMS NOTED EXCEPT A FEW SMALL OIL LEAKS AND 2 CRACKED CYLINDERS WHICH WERE REPAIRED PRIOR TO THIS FLT. I FEEL VERY STRONGLY THAT AN AIRWORTHINESS DIRECTIVE BE ISSUED TO BE SURE ALL FLUID CARRYING HOSES BE CHANGED EVERY 5 YRS REGARDLESS OF HRS ON ALL TURBO-CHARGED ACFT. ALSO; A PLACARD BE APPLIED BY MANIFOLD PRESSURE GAUGES TO NOTE THAT IF AN UNEXPLAINED MANIFOLD PRESSURE DROP IS NOTED EXCEEDING 3 INCH ENG BE SHUT DOWN AND LAND AS SOON AS PRACTICAL (ON TURBO-CHARGED ACFT). I HAVE HAD EXHAUST LEAKS DEVELOP AND ALMOST BURN A HOLE IN COWLING. THE 50 HR INSPECTION IS OK BUT THERE IS A LOT OF OLD BRITTLE EXHAUST SYS FLYING AROUND. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES NO WAY TO REALLY DETERMINE CAUSE OF FIRE BUT HE HAS A 'GUT' FEELING ABOUT THE FLUID CARRYING HOSES ON OLDER TURBO CHARGED ACFT. BELIEVES 5 YR REQUIRED REPLACEMENT WOULD HELP SOLVE/PREVENT SITUATIONS LIKE HIS. HE KNOWS OF OTHERS WHO WERE NOT SO LUCKY AS HE AND NEVER MADE IT TO A SAFE LNDG. IDEA OF A PLACARD BY MP GAUGE IS ANOTHER SAFETY FACTOR TO CONSIDER.