I have flown my C-4 quite a bit. It has been powered by a T-tiger Pro .36 2-stroke and an O.S. 40 4-stroke. I like it because I have a dumb left hand and the C-4 turns nicely using rotor tilt alone.

I think the 4 rotor blades generate more drag as well as more lift. My blades turn slow enough you can almost see them as it flies along. If I suddenly chop the power, or the engine quits, it does have a tendency to nose up abruptly. This can be controlled with application of down elevator. In fact Steve Tilison saw some photos I sent him of mine in flight and was amazed at the nose down angle I was using to maintain blade rpm on a dead stick landing! On the up side, my rotor spins into autorotation quickly and I can fly on very low throttle settings.

Check with Steve, but I think if you replaced the 4 blade rotor with a 3 blade rotor, the model would be less likely to pitch up when it slows down.