I use E3 in mine. Aside from the light knock (due I think to running on original oil fill for over 50 hours.... ) it runs great. The E3 reduced fuel consumption quite a bit. (Previously by the time I finished our yard with a full tank of gas (I always fill it so when I put the cap on, it pushes a little bit out) it would be bone dry at the bottom of the tank. After the E3 plug, There is a good 1/4 inch of gas left at the bottom of the tank. Also, it starts much faster and easier, and it seems to have more power when mulching tall grass.