Narrative:

My student and I were on a flight. We had had the engine stumble a couple of times the previous day and it had cleared up after applying the choke (the engine is a rotax 914). While in our descent the engine started sputtering quite a bit. I turned on the fuel pump and it got worst - so I turned it off. The engine would start to quit and then start back up. We declared and emergency and flew the last 6 miles with little power and landed. We did have another aircraft in the pattern that did not seam to hear our emergency call - another aircraft called him and advised him of the situation and then he broke off his approach so we could land. Upon landing the engine quit. We checked and found a small leak around the fuel pressure sensor in the engine area. The next day we flew the aircraft to a rotax maintenance facility and were told by the rotax expert there that the fuel system had several 'artful engineering' type of changes to the rotax system. The rotax expert stated some of the following needed to be corrected with the aircraft: fuel pumps need to be run in series rather than parallel as rotax recommends: otherwise this can cause vapor lock. Fuel pumps need to be moved out of engine compartment otherwise they are prone to heating up: this also can cause vapor lock. Excessive fuel burn needs to be diagnosed and fixed which may be due to fuel return being connected into the carburetor: this also can cause vapor lock. Fuel return needs to be disconnected from carburetor and fuel return lines need to be installed into both left and right tanks as rotax recommends: otherwise this can cause vapor lock. A dual type fuel selector needs to be installed that will return the fuel to the fuel tank selected. The cause of high fuel pressure needs to be diagnosed and fixed (may be due to fuel return into the carburetor): otherwise this can cause vapor lock and lead to fuel leaking through the fuel line clamps as was the case we experienced and may be partially responsible for the excessive fuel usage. Incorrect fuel pressure gauge rendered fuel pressure information useless. The aircraft was left at the airport and the manufacturer was contacted about the unsafe condition of the aircraft. The manufacturer later picked up the aircraft and the owner has asked for a refund.

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Original NASA ASRS Text

Title: A Sirus TL-3000 engine began erratic operation while at cruise so the pilot declared an emergency and landed at a nearby airport. The fuel system was found to have several irregular modifications which could lead to vapor locks.

Narrative: My student and I were on a flight. We had had the engine stumble a couple of times the previous day and it had cleared up after applying the choke (the engine is a Rotax 914). While in our descent the engine started sputtering quite a bit. I turned on the fuel pump and it got worst - so I turned it off. The engine would start to quit and then start back up. We declared and emergency and flew the last 6 miles with little power and landed. We did have another aircraft in the pattern that did not seam to hear our emergency call - another aircraft called him and advised him of the situation and then he broke off his approach so we could land. Upon landing the engine quit. We checked and found a small leak around the fuel pressure sensor in the engine area. The next day we flew the aircraft to a Rotax maintenance facility and were told by the Rotax expert there that the fuel system had several 'artful engineering' type of changes to the Rotax system. The Rotax expert stated some of the following needed to be corrected with the aircraft: Fuel pumps need to be run in series rather than parallel as Rotax recommends: Otherwise this can cause vapor lock. Fuel pumps need to be moved out of engine compartment otherwise they are prone to heating up: this also can cause vapor lock. Excessive fuel burn needs to be diagnosed and fixed which may be due to fuel return being connected into the carburetor: This also can cause vapor lock. Fuel return needs to be disconnected from carburetor and fuel return lines need to be installed into both left and right tanks as Rotax recommends: Otherwise this can cause vapor lock. A dual type fuel selector needs to be installed that will return the fuel to the fuel tank selected. The cause of high fuel pressure needs to be diagnosed and fixed (May be due to fuel return into the carburetor): Otherwise this can cause vapor lock and lead to fuel leaking through the fuel line clamps as was the case we experienced and may be partially responsible for the excessive fuel usage. Incorrect Fuel Pressure gauge rendered fuel pressure information useless. The aircraft was left at the airport and the manufacturer was contacted about the unsafe condition of the aircraft. The manufacturer later picked up the aircraft and the owner has asked for a refund.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.