A PA-24 on a break-in test flight after cylinder changes; ran out of fuel and glided into a nearby Class C airport. The aircraft had a fuel line leak and the fuel flow was unusually high because of the new engine components.

Narrative

I was contacted by the owner of the aircraft to help him break-in his new cylinders and test fly the aircraft after 5 months of no activity. I had no previous experience in the type of aircraft but I have experience in engine break-in procedures. We met at the aircraft and discussed our plan. We would fly the aircraft for 2-3 hours at 75 percent power as per the Lycoming Service Bulletin. We elected to stay near airports for the duration of the flight in case any unforeseen problems arose. We filled the main tanks with full fuel giving us a total of 60 gallons. We estimated the engine would burn 15-17 GPH at full rich at 75-65 percent between 3;500-4;500 FT. It typically burns 12-14 GPH at the same power settings using a rich of peak leaning technique. The Aircraft POH did not have a published fuel burn for our power settings with a full rich mixture. We completed a thorough preflight and engine run up with no anomalies and climbed to 4;500 FT and set 75 percent power with no sign of problems. We circled overhead the airport for an hour and then continued south to overfly a few close airports. At about 1:30 minutes into the flight I noticed the fuel gauges were reading low. I questioned the owner and his reply was 'the gauges always read low in this airplane; they are unreliable.' Having no previous experience in this model/type of aircraft I assumed that since he has experience in his own aircraft and that being a normal indication it was acceptable to continue the flight. At approximately 2 hours into the flight we were 5 miles from ZZZ at 3;500 FT. At this time the engine began to surge; we began to troubleshoot the problem thinking it was the propeller governor. After about 10 seconds the engine power reduced to idle with occasional surging. The owner gave me the flight controls. I immediately turned to ZZZ and established the best glide speed. I notified ATC we were experiencing engine trouble and were heading to ZZZ. I began troubleshooting by checking the fuel tank selectors; the primer; the mixture; and the electric fuel pump. The engine regained power when the electric fuel pump was activated but only momentarily. I pumped the primer repeatedly and was able to regain some power for only a few seconds. At this time I elected to pull the propeller control to reduce the propeller RPM and increase glide distance. There was no fuel in the tip tanks according to the owner. By my own estimation we would make the airport but were too low to land on any runway. I elected to land on Taxiway C as we were in a position to land straight in to that taxiway. I was concerned however that we wouldn't have enough distance to stop. As we crossed the airport boundary it became clear that we had enough altitude to turn a short and low final to line up with Runway 30L. I instructed the owner to put the gear down and I turned final at the same time. The gear came down and I leveled the wings and flared. We touched down smooth and were able to taxi off the runway at Delta. The aircraft was towed to an FBO and we inspected the aircraft and found both main tanks to be dry. We had a Mechanic inspect the aircraft and he found signs of possible fuel streaking back along the belly. The Mechanic was able to tighten a loose fuel hose leading to the electric fuel pump and there were signs of blue streaking in this area. We fueled the aircraft with 20 gallons and ran the engine under various power conditions with the Mechanic looking visually for leaks. The Mechanic was not able to see any visual signs of leaks and said the aircraft was ok to fly back to the home base only 5 miles away for further inspection. We completed that short flight uneventfully. Upon further reflection I believe the contributing factors to the fuel starvation were three fold: an unusually high fuel burn that we did not anticipate; a fuel leak; and improper planning. We should have filled the tip tanks with fuel prior to departure even though we were not anticipating the need for them to account for all possible circumstances. Unusually high fuel flow is common on engine break-ins and I did not estimate it properly; this is due to my unfamiliarity with this make of aircraft. We should have started with a flight of shorter duration to check for leaks or any anomalies that could not be detected in the air. I should have insisted we land after noticing low fuel tank indications regardless of what the owner had said. Any of these things would have prevented this situation from happening in the first place. I will take what I have learned from this situation and use it to ensure that I never get into this circumstance again.