try going down the side of a welsh mountain without a front brake
If your happy with the brakes and suspension then you need more power.
The best power upgrade for a 140 is a port and polish DIY, take the head off and take it apart, get some sand paper and polish the ports and inlet manifold.
If you have a dremel you can port it too, but be careful.
Re seat the valves.
the best upgrade for power I found was doing that.