Sinergy nailed what I was trying to say quite well. See if there's something that's being missed in carb tuning to bring the rpm up. Unless there's some untapped rpm in that engine you're not getting your money's worth even at a cost much less than it is. I don't know the engine at all, but a 100cc engine should be providing more power than a 70 or 80. If it does not, then you are suffering a penalty for the weight of the larger engine while sacrificing the power of a smaller one. You might want to see what happens with a more efficient prop while you're at it. The Top Flite will tend to be rather low on the performance level. It's easy to see why when the engine is running. Change the rpm levels and watch the prop arc. You'll like as not see that Top Flite flex forward and back quite a bit with the rpm cycles. That's nothing but lost power.

Play with it a bit and let us know how it all turns out as it breaks in. It would be nice to see a less expensive 100 that came close to all the others.