Date: 201209
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Mission: Personal
Flight phase: Cruise
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Flight Instructor
Human factors: Training / Qualification; Troubleshooting; Confusion; Distraction; Situational Awareness; Time Pressure
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Took Evasive Action; Flight Crew Returned To Departure Airport; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Became Reoriented; General Declared Emergency
Contributing factors: Human Factors; Aircraft; Procedure
Primary problem: Ambiguous

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.




Synopsis: 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.