LSA pilot reports engine failure while returning to the airport after conducting a Discovery Flight with a passenger. When it is discovered that the airport cannot be reached a grassy field is chosen and a successful off airport landing ensues. No damage results.

Narrative

I was conducting a discovery flight. Prior to start the engine I completed a through pre-flight inspection. After engine start I let it warm up for 10 minutes. Then I was on hold by the Ground Control another 5 minutes due to heavy traffic. The engine run up and take off was normal. We flew 10 miles west of the airport for the sight seeing discovery flight. There was no indication of any kind of engine trouble. During our flight back to the airport; 2.5 miles from the airport the aircraft engine started to surge up and down. I performed checklist items for emergency and verified all items need to be checked and secured. Then about 20 seconds later engine completely stopped running. I declared emergency and set up for a power off landing to the airport. I tried to restart the engine. It started for 10 seconds and started to surge again and shut off again. Then I briefed the passenger for emergency landing. I started to lose altitude and I realized that I did not have enough altitude to glide to the airport safely. So; after a quick search I found a remote grassy field suitable for a safe landing west of the airport. I used 65 MPH recommended by the aircraft POH glide airspeed and landed safely. Then I called ATC to let them know our location and we are safe. There was no damage to the aircraft and no bodily injury to the passenger. In the future I will be attending safety seminars held by local FAA offices.