BC-12 Taylorcraft pilot reported an engine failure during cruise with an off-field landing. Pilot reported no injuries or damage.

Narrative

I conducted a local flight as pilot in command of Taylorcraft BC-12D departing from ZZZ with a planned return into ZZZ about 3 hours after departure. During preflight; I determined the weather; conditions; and other flight sensitive information to be flight permitting. A routine preflight inspection was conducted and nothing was observed to be out of order. After engine start; I preformed an engine run-up and verified that both magnetos were functional as well as carburetor heat. After determining that the engine was functioning per normal specification I received taxi and takeoff clearances from the ZZZ control tower. I departed westbound until leaving ZZZ surface area where I then terminated radar services and continued northbound. My intentions for this flight were to practice ground reference maneuvers around the large farmland area south. At approximately 15nm south of ZZZ1 at an altitude of 2;000'MSL the engine made a distinct sputtering sound followed by a significant RMP drop. Recognizing the situation as an engine failure; I established best glide speed and chose an adequate field for landing. As I was maneuvering to execute an emergency landing I attempted to diagnose and restart my engine; verifying that the magnetos were on the 'BOTH' position; primer was in and to the locked position; the fuel selector set to the main tank; and observed that the fuel shutoff valve appeared to be in the operating position. Due to the lack of an electronic starter; I had little time to attempt an engine restart before the engine stopped movement entirely. After all engine movement had stopped; I set the magnetos to the 'OFF' position as part of the emergency landing checklist. After this had been completed; I determined there was adequate time to contact ATC on guard. After requesting priority handling on the guard frequency; I was instructed to contact ZZZ approach. I supplied ATC with the needed information such as nature of situation; location; altitude; souls on board and aircraft color. I proceeded to execute a landing with no further incident. After safely executing the emergency landing without harm to myself or the aircraft; I exited the aircraft to call ZZZ Approach and inform them of the situation. I then completed an inspection of the engine and cabin to attempt to diagnose the engine failure. It was only at this point that I observed the fuel shutoff valve to be partially set to the off position. This configuration did not provide adequate fuel to the engine whilst also being minor enough to remain unseen. After assessing the situation; receiving clearance from the landowner and authorities to depart from the field and making adequate adjustments to the fuel shutoff valve; I determined that a safe return to ZZZ could be made. After departing from the field; I observe the fuel shutoff valve to operate as intended and continued to ZZZ without any further incident. After landing at ZZZ; I preformed another post flight inspection and did not observe any malfunctioning equipment or mechanical failures and verified the aircraft is functional and safe. two additional flights accumulating for 8.2 hours were conducted without incident. Upon further reflection; a more thorough examination of the fuel shutoff valve during preflight and during the emergency checklist may have prevented an occurrence. I am lead to believe that some sort of vibration may have caused the fuel shutoff valve to partially disengage as I observed the valve to be in the fully on position during preflight.