The pilot was to conduct two spot landings from practice forced landing approaches commenced at 2000 feet. On the first approach an undershoot developed and power was used to complete the landing. The second approach was high and touchdown was made about half way down the 730 metre strip. A go-around was initiated but the engine failed to develop significant power. The take-off was then abandoned and the aircraft struck a dirt bank and drain beyond the end of the strip. It is probable that carburettor icing caused the lack of engine response when the go-around was initiated. Braking was inhibited by wet grass covering the remainder of the strip available.