Date: 201501
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Amateur/Home Built/Experimental
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Takeoff / Launch
Airspace: Class G ZZZ
ATC / advisory: UNICOM ZZZ
Aircraft component: Engine
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying
Reporter qualification: Flight Crew Commercial
Human factors: Human-Machine Interface
Anomaly: Aircraft Equipment Problem Critical; Ground Incursion Taxiway; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: After takeoff on runway 05 at approximately 100 ft at full power; I experienced a surge in engine power. The engine continued to surge from 900-1000 rpm to 2400 rpm (full power). The aircraft was in a climb attitude at approximately 1400 fpm climb. As the engine surged; the aircraft would continue to climb; then when the engine lost power; the aircraft would descend. I was able to turn to set up a landing on the closed runway used by the Radio controlled aircraft club; however I was too fast (110mph) and too close in to make that runway. I then continued on to land on the remaining portion of that runway however; just at touch down; the engine again surged to full power and the aircraft entered a steep climb. At this time I was over the [condominium hangars] area of the airport at approximately 100 ft. and 120 mph. The engine continued to run at climb power for several seconds before quitting again. While under power; I was able to turn for an intended landing on runway 05 however the engine lost power again at just short of alignment with the runway so I extended the speed brake and executed a normal landing on taxiway alpha. There were no other aircraft operating either in the air or on the ground at the airport at the time. Upon a normal taxi to the run up area at the east end of the airport; I stopped the aircraft to evaluate the situation and determine the cause of the engine surge. I discovered the fuel valve to be set on the main fuel tank (as is normal for takeoff) however it was out of the detent and partially closed; restricting full fuel flow to the engine. This condition caused the power surges as the carburetor bowl would fill (full power) then use the fuel and cut off as the bowl would refill for the next surge. The aircraft is equipped with a main (header) tank holding 22 gal with 21.5 gal useable and had 17.5 gal on board at the time. The fuel valve has been removed at this time and will be replaced with a fuel valve with a spring loaded position locking pin instead of a decent to prevent a partial on condition. As an experienced experimental aircraft builder and test pilot I have become familiar with this type of test flight and always conduct test flights at low activity times at the airport and announce over Unicom that I am conducting a test flight and may need to use an alternate runway to land. This test flight was conducted with full safety in mind with an on ground observer; fire extinguisher and following published test flight procedures.




Synopsis: When the power on the pilot's experimental aircraft started to surge dramatically between barely running and full power shortly after takeoff he maneuvered during powered surges to align with and land safely on a taxiway at the airport. Post flight examination determined the fuel tank selector valve was not in the detent thus restricting fuel flow to the engine.