SMA HAS ENG MISFIRE THEN SURGE. OFF ARPT LNDG.

Narrative

WHILE IN CRUISE VFR AT 8500 FT THE ENG STARTED TO MISFIRE; DIE DOWN; THEN SURGE BACK. THE SOUND WAS POPPING AND BANGING. I THOUGHT IT WAS A VALVE OR PISTON. THIS WAS A NEWLY OVERHAULED ENG. I CALLED RALEIGH APCH; DISCUSSED AND GOT VECTORS TO 'RALEIGH EAST' ARPT. I TRIED SWITCHING TANKS BACK AND FORTH I BELIEVE AND HAD PUT ON BOOSTER PUMP BUT NO SUCCESS IN RESTARTING. WE GLIDED TO JUST SHORT OF RALEIGH EAST ARPT AND MADE SMOOTH LNDG IN FIELD. SHORT FIELD; WHEELS UP. DAMAGED PROP AND BELLY. I SUSPECT CAUSE TO BE FUEL RELATED. HAD RUBBER BLADDER TANKS INSTALLED SEVERAL YRS AGO WHICH HAVE 3 CELLS IN EACH WING. WHEN FUELING; THERE IS A TRICKLE DOWN FACTOR. I HAVE BEEN GETTING 2 HRS 25 MINS OUT OF EACH SIDE TANK WITH NO PROB OR STARVATION. TODAY; ENG FAILED AT 1 HR 45 MINS OUT. RECOMMEND THAT INSTALLER MUST SUPPLY ACCURATE FUEL INDICATOR; GAUGES; BLINKING RED LOW FUEL LIGHTS OR SOMETHING WITH THIS STC CONVERSION -- WHETHER OR NOT THIS WAS THE PROB. PERHAPS IT WAS ANOTHER MECHANICAL PROB. OUR MECHS WILL TRY TO DETERMINE CAUSES IN THE NEAR FUTURE.