Hobbsy, Ah...but I bet they "could" be made to make a lot more power. Let's face it, 2 intake valves will flow more than 1 , given the same area in the head. (more surface area). Maybe the one's you have don't have the cam needed to make the horse power. Most 4 stroke engines are capable of more power than what the designer wanted it to make for reliability. It's a shame that someone out there doesn't make a couple of different grinds, maybe for torque, mid-range and top end for our engines. Just a thought.
Suptter