The latest bits for a case reed CR250 make a awesome engine (about 70hp at the wheel on pump fuel that's real clydesdales not a figure someone plucked out of the air) or the WIWA 68 X 68mm Gas Gas 250 that apparently has cracked the 80hp mark. Don't even think for a second think they are a peaky all or nothing power delivery either. Both of those engines are used in 250 National superkarts.