Narrative:

I took off and was turning left downwind for a north departure when my engine sputtered. I elected to return to the field and land opposite direction. On the return I selected carb heat on; checked mixture rich; checked boost pump on and changed fuel tanks. My engine sputtered a second time as I was completing my turn back to the field. I maintained energy as best I could and landed with a high energy state and rolled off the active runway onto the overrun. It's possible I could have avoided using the overrun if I had braked harder; but I didn't want to skid; lock or blow a tire. I selected mixture to cutoff and fuel tank off when I knew I had enough energy to roll off the runway and onto the taxiway. Emergency vehicles met me on the taxiway and after a break I tried to restart the engine and taxi back to parking. The motor hesitated and after subsequently talking to the fire chief I decided to be towed back instead.it appears the power loss was due to water contamination in the fuel system. Before the flight I drained a full vial of fuel from both sumps; and there was no sign of contamination (no bubbles; no discoloration). Further; the engine ran well for 15-20 minutes prior to losing partial power. (I taxied 2 miles to the end of the runway and performed a full run-up once there with no evidence of engine problems) however; after the flight I let the aircraft sit overnight and then resampled the fuel tank sumps and gascolator. All three samples contained water. I didn't believe it at first; but water was clearly in the vial after each sample (which I had never seen before but was obvious). The difference was in the method I used to sample the fuel. The day of the incident I had checked the fuel with the nose gear extended. This (unbeknownst to me at the time) had precluded the sumps from being at the bottom of the fuel system; which caused the water to migrate away from the sumps. Additionally; the gascolator didn't show contamination prior to flight because fuel hadn't migrated down to that part of the fuel system as I had the fuel selector positioned off. The day after the incident I resampled the sumps and gascolator with nose gear retracted and later with nose gear extended. I found evidence of water when I checked it with nose gear retracted but not when the nose gear was extended. So my fuel contamination check was previously flawed which prevented me from discovering the fuel contamination. Incidentally; I believe the contamination entered the fuel system through the tank vents during a wash. I had [a company] wash the aircraft; and I requested they do so when I was present. However; they did not contact me prior to washing the aircraft; so I was not there to observe them. Knowing this; I drew several vials of fuel afterwards and I had ran the aircraft on the ground three times before flying. No previous samples contained water; and the engine ran well. However; this was likely due to my flawed sampling procedure. The day I lost power the water in the fuel system was able to make its way to the engine as I turned crosswind/downwind and put the airplane in the proper attitude to migrate the water to the pick-ups inside the tank.

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Original NASA ASRS Text

Title: Long EZ pilot experiences a rough running engine turning downwind after takeoff and returns to land opposite direction on the departure runway. Post flight reveals that water was the likely cause and that sumping the Long EZ with the nose gear extended does not put the drains at the lowest point; so the water went undetected.

Narrative: I took off and was turning left downwind for a north departure when my engine sputtered. I elected to return to the field and land opposite direction. On the return I selected carb heat on; checked mixture rich; checked boost pump on and changed fuel tanks. My engine sputtered a second time as I was completing my turn back to the field. I maintained energy as best I could and landed with a high energy state and rolled off the active runway onto the overrun. It's possible I could have avoided using the overrun if I had braked harder; but I didn't want to skid; lock or blow a tire. I selected mixture to cutoff and fuel tank off when I knew I had enough energy to roll off the runway and onto the taxiway. Emergency vehicles met me on the taxiway and after a break I tried to restart the engine and taxi back to parking. The motor hesitated and after subsequently talking to the fire chief I decided to be towed back instead.It appears the power loss was due to water contamination in the fuel system. Before the flight I drained a full vial of fuel from both sumps; and there was no sign of contamination (no bubbles; no discoloration). Further; the engine ran well for 15-20 minutes prior to losing partial power. (I taxied 2 miles to the end of the runway and performed a full run-up once there with no evidence of engine problems) However; after the flight I let the aircraft sit overnight and then resampled the fuel tank sumps and gascolator. All three samples contained water. I didn't believe it at first; but water was clearly in the vial after each sample (which I had never seen before but was obvious). The difference was in the method I used to sample the fuel. The day of the incident I had checked the fuel with the nose gear extended. This (unbeknownst to me at the time) had precluded the sumps from being at the bottom of the fuel system; which caused the water to migrate away from the sumps. Additionally; the gascolator didn't show contamination prior to flight because fuel hadn't migrated down to that part of the fuel system as I had the fuel selector positioned off. The day after the incident I resampled the sumps and gascolator with nose gear retracted and later with nose gear extended. I found evidence of water when I checked it with nose gear retracted but not when the nose gear was extended. So my fuel contamination check was previously flawed which prevented me from discovering the fuel contamination. Incidentally; I believe the contamination entered the fuel system through the tank vents during a wash. I had [a company] wash the aircraft; and I requested they do so when I was present. However; they did not contact me prior to washing the aircraft; so I was not there to observe them. Knowing this; I drew several vials of fuel afterwards and I had ran the aircraft on the ground three times before flying. No previous samples contained water; and the engine ran well. However; this was likely due to my flawed sampling procedure. The day I lost power the water in the fuel system was able to make its way to the engine as I turned crosswind/downwind and put the airplane in the proper attitude to migrate the water to the pick-ups inside the tank.

Data retrieved from NASA's ASRS site 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.