Narrative:

Was taking a friend up interested in taking lessons. I have never given primary instruction; so this was more of a familiarization ride. Aircraft is technically experimental. Varga kachina modified with bubble canopy; tailwheel; O-320I etc. Little background. One of partners in this aircraft lost control couple years back on takeoff. Banged it up extensively. Aircraft rebuilt. Engine rebuilt. Ever since we've gotten it flying again it has run rich. If you don't lean; it will burn approximately 10.5-11 gal/hr. Should burn no more than 9; maybe under 8 leaned out at altitude. So consequently we've been leaning it out more than usual. Probably had it too lean today at 4;000 ft. [I was] demonstrating slow flight handling characteristics when we lost power. Vapor lock? Not sure but I immediately increased mixture to nearly full rich; takeoff position about one finger out. Was monkeying around with power trying to keep it running as engine was sputtering I was working throttle trying to keep it going. Immediately turned toward closest airport and declared [an] emergency. At first [I] wasn't sure I would make [the] airport about 7-8 miles away. But with partial power had a low enough descent rate that I realized I could make it. Was able to eventually restore power. Then I terminated emergency and returned to home field. Even though I terminated; [I] was met by one fire truck upon return. Called tower said no report necessary. I did tell them on way in that I did not require ATC prioritization and that I had terminated emergency. I realized later I should have immediately turned on boost pump which probably would have restored full power. Heat of the moment; we humans make mistakes. Even those of us with experience. Although I did check shut off valves; mixture etc. I may have instigated this emergency by running the engine too lean; slowing airplane down with reduced airflow and too lean of a mixture? I don't believe the sputtering was detonation (no loud bangs that I remember) but would love input. My experience has taught me to fly the airplane first and suck it up (declare emergency). I will never hesitate because I know you have all the protections in the world (license) once you use the e-word. The tower I initially headed for was very helpful clearing me in to land opposite direction but I was able to restore power about 3 miles from field.

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Original NASA ASRS Text

Title: A Varga Kachina pilot declared an emergency and started to divert to a nearby airport because of an engine malfunction; but after turning the fuel boost pump ON flew safely to his home airport.

Narrative: Was taking a friend up interested in taking lessons. I have never given primary instruction; so this was more of a familiarization ride. Aircraft is technically experimental. Varga Kachina modified with bubble canopy; tailwheel; O-320I etc. Little background. One of partners in this aircraft lost control couple years back on takeoff. Banged it up extensively. Aircraft rebuilt. Engine rebuilt. Ever since we've gotten it flying again it has run rich. If you don't lean; it will burn approximately 10.5-11 gal/hr. Should burn no more than 9; maybe under 8 leaned out at altitude. So consequently we've been leaning it out more than usual. Probably had it too lean today at 4;000 FT. [I was] demonstrating slow flight handling characteristics when we lost power. Vapor Lock? Not sure but I immediately increased mixture to nearly full rich; takeoff position about one finger out. Was monkeying around with power trying to keep it running as engine was sputtering I was working throttle trying to keep it going. Immediately turned toward closest airport and declared [an] emergency. At first [I] wasn't sure I would make [the] airport about 7-8 miles away. But with partial power had a low enough descent rate that I realized I could make it. Was able to eventually restore power. Then I terminated emergency and returned to home field. Even though I terminated; [I] was met by one fire truck upon return. Called Tower said no report necessary. I did tell them on way in that I did not require ATC prioritization and that I had terminated emergency. I realized later I should have immediately turned on boost pump which probably would have restored full power. Heat of the moment; we humans make mistakes. Even those of us with experience. Although I did check shut off valves; mixture etc. I may have instigated this emergency by running the engine too lean; slowing airplane down with reduced airflow and too lean of a mixture? I don't believe the sputtering was detonation (no loud bangs that I remember) but would love input. My experience has taught me to fly the airplane first and suck it up (declare emergency). I will never hesitate because I know you have all the protections in the world (license) once you use the E-word. The Tower I initially headed for was very helpful clearing me in to land opposite direction but I was able to restore power about 3 miles from field.

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.