Citabria 7ECA pilot reported he lost fuel out of a tank that had the cap improperly secured.

Attributes
ACN	1303301
Time
Date	201510
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Champion Citabria 7ECA
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	None
Component
Aircraft Component	Fuel Tank Cap
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Private
Experience	Flight Crew Last 90 Days 5 Flight Crew Total 173 Flight Crew Type 24
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Inflight Event / Encounter Fuel Issue

Narrative:

After conducting a pleasure flight to [ZZZ]; I refueled the aircraft at [ZZZ] prior to starting my return trip to [ZZZ1]. Approximately 20 minutes into the flight; having climbed to my cruise altitude of 3;500 feet; I observed that while my right fuel gauge read full as expected; the left gauge was reading about 3/4 of a tank. I immediately diverted to the nearest airport [ZZZ2]; (about 15nm from my position when I noticed the issue) for a precautionary landing. Upon landing; I discovered a large amount of blue dye stains on the right wing; and that the right fuel cap was slightly crooked. When I physically removed and reinstalled the cap; it was no longer crooked. Despite double-checking the caps after fueling at [ZZZ1]; I did not notice the issue with the cap at that time.based on the amount of fuel I added at [ZZZ2] to top off the aircraft (~14 gallons) and the approximate duration of the flight; I believe that I was losing a gallon of fuel overboard about every 2-3 minutes; and that when I landed at [ZZZ2]; I had approximately 10 minutes of fuel remaining in the left tank.

Original NASA ASRS Text

Title: Citabria 7ECA pilot reported he lost fuel out of a tank that had the cap improperly secured.

Narrative: After conducting a pleasure flight to [ZZZ]; I refueled the aircraft at [ZZZ] prior to starting my return trip to [ZZZ1]. Approximately 20 minutes into the flight; having climbed to my cruise altitude of 3;500 feet; I observed that while my right fuel gauge read full as expected; the left gauge was reading about 3/4 of a tank. I immediately diverted to the nearest airport [ZZZ2]; (about 15nm from my position when I noticed the issue) for a precautionary landing. Upon landing; I discovered a large amount of blue dye stains on the right wing; and that the right fuel cap was slightly crooked. When I physically removed and reinstalled the cap; it was no longer crooked. Despite double-checking the caps after fueling at [ZZZ1]; I did not notice the issue with the cap at that time.Based on the amount of fuel I added at [ZZZ2] to top off the aircraft (~14 gallons) and the approximate duration of the flight; I believe that I was losing a gallon of fuel overboard about every 2-3 minutes; and that when I landed at [ZZZ2]; I had approximately 10 minutes of fuel remaining in the left 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.