BE55 PLT SUFFERS PARTIAL POWER LOSS OF LEFT ENGINE.

Narrative

WHILE WE WERE IN CRUISE FLT; THE L ENG LOST PWR. I HAD SWITCHED FROM THE L AUX TANK TO THE L MAIN TANKS. I HAD FLOWN ABOUT 1 HR 50 MINS ON THE L AUX TANKS WHEN I SWITCHED BACK TO THE L MAIN TANK. I RECALL POTOMAC APCH GAVE ME A LOWER ALT FROM 11000 FT TO 10000 FT. I NOTICED AFTER LEVELING OFF AT 10000 FT; WITH THE SAME PROP AND THROTTLE POS; THE L FUEL FLOW STARTED FLUCTUATING MORE THAN NORMAL. I DID NOTE THAT I HAD BEEN FLYING FOR 5-7 MINS WHEN I SWITCHED TANKS. I NOTICED THE FUEL FLOW WAS DECREASING MORE AND THE L ENG BEGAN TO SURGE. AFTER THE PWR LOSS; I MADE SURE THE THROTTLES WERE FULL FORWARD AND I PUSHED THE MIXTURES SLIGHTLY MORE RICH AND I PUSHED THE PROPS FORWARD TO 2500 RPM. I CHKED MY FUEL SELECTOR AND MADE SURE I WAS ON THE L MAIN FUEL TANK -- AND I WAS ON THE L MAIN FUEL TANK -- ALSO TURNED THE FUEL BOOST PUMP TO LOW. I THEN CHKED BOTH MAGNETOS AND THIS DID NOT HELP. I THEN SWITCHED BACK TO THE L AUX TANK AND THIS DID NOT HELP; AND THEN SWITCHED BACK TO THE L MAIN TANK. THE ENG WAS STILL TURNING AT 2200 RPM'S AND WHEN I MOVED THE THROTTLE; THE RPM'S WOULD CHANGE AND THE PLANE WOULD YAW MORE TO THE L; SO I KNEW THE ENG WAS MAKING SOME PWR. I THEN MOVED THE FUEL BOOST PUMP TO HIGH AND AT THIS TIME THE ENG COMPLETELY LOST PWR. I TURNED THE BOOST PUMP OFF AND MOVED THE FUEL SELECTOR TO XFEED TO SEE IF THIS WOULD HELP. AFTER A MOMENT; THE L ENG REGAINED PWR AND SURGED 2 MORE TIMES BEFORE REGAINING NORMAL PWR. AFTER I WAS SURE THE PLANE WAS RUNNING NORMAL; I CONTINUED MY FLT TO ZZZ ON THE XFEED. AT THIS TIME THE PLANE WAS RUNNING NORMAL AND I KNEW I HAD ENOUGH FUEL IN THE R MAIN FUEL TANK TO CONTINUE MY 20-25 MIN FLT TO ZZZ. IN THE MEANTIME; I DECLARE AN EMER AND WAS STANDING BY FOR VECTORS TO ZZZ2. I CONTINUED TO ZZZ WITH NO MORE PROBS. THE NEXT DAY I HAD AN AVIATION MECH LOOK AT MY PROB. THE MECH DID FEEL IT WAS A FUEL PROB AND DID A COMPLETE CHK OF THE FUEL SYS TO HIS KNOWLEDGE AND PER A MAINT MANUAL NOTING NO ABNORMAL PROB. HE FEELS LIKE IT WAS AIR IN THE FUEL SYS THAT CAUSED THE ENG TO SURGE. HE DID AN ENG RUN-UP AND CLRED THE PLANE WAS SAFE FOR FLT. WHEN I FUELED UP; THE L AUX TANK WAS FILLED WITH 28.8 GALLONS WITH 2.2 LEFT IN A 31.0 USABLE GALLON. THE L MAIN TANK WAS FILLED WITH AROUND 7 GALLONS OUT OF 37 USABLE GALLONS IN THE L MAIN FUEL TANK.