Narrative:

Ten minutes after departing [from a refueling stop] the engine RPM started to decay from 2;500 to 2;350. Adjusted mixture to rich and engine became rough and RPM fluctuated between 1;900 and 2;300 RPM. Found a likely landing spot on paved highway and set up glide and ran engine fail in-flight checklist; changed tanks; boost pump on; mixture rich; throttle idle; at that point engine started to run better but not normally. I made initial contact with center; on the flight following frequency I have used prior to starting approach to [the airport]. Controller answered. I informed him I was having engine trouble and declared an emergency. I told him I was planning on landing on the paved highway below. He initially asked for position and altitude; gave me a squawk and tried to locate us. Sometime later fuel and souls on board (sob). He was unable to locate us and I gave him coordinates. During this time; I kept trying to get power from the engine; sometime during initial contact; after trying several combinations of throttle and mixture settings the engine started running normally. I suspected fuel contamination; and whatever was causing the problem passed through the system. After determining the engine was providing normal power; I informed the controller; I was going to try to make an airstrip further [along my route. I was eventually able to climb up to 11;500 ft and continue to my destination; always with an airport in gliding range but no further problems occurred.]

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Original NASA ASRS Text

Title: RV-9 pilot reports loosing power ten minutes after takeoff from a fuel stop. The engine continues to make power and a landing on a highway is delayed in hopes of landing at an airport. Before that can happen the engine begins to run normally again and the flight continues to destination.

Narrative: Ten minutes after departing [from a refueling stop] the engine RPM started to decay from 2;500 to 2;350. Adjusted mixture to rich and engine became rough and RPM fluctuated between 1;900 and 2;300 RPM. Found a likely landing spot on paved highway and set up glide and ran Engine Fail In-flight Checklist; changed tanks; boost pump on; mixture rich; throttle idle; at that point engine started to run better but not normally. I made initial contact with Center; on the flight following frequency I have used prior to starting approach to [the airport]. Controller answered. I informed him I was having engine trouble and declared an emergency. I told him I was planning on landing on the paved highway below. He initially asked for position and altitude; gave me a squawk and tried to locate us. Sometime later fuel and Souls On Board (SOB). He was unable to locate us and I gave him coordinates. During this time; I kept trying to get power from the engine; sometime during initial contact; after trying several combinations of throttle and mixture settings the engine started running normally. I suspected fuel contamination; and whatever was causing the problem passed through the system. After determining the engine was providing normal power; I informed the Controller; I was going to try to make an airstrip further [along my route. I was eventually able to climb up to 11;500 FT and continue to my destination; always with an airport in gliding range but no further problems occurred.]

Data retrieved from NASA's ASRS site as of July 2013 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.