The cam has a weight that is on a lever. That lever turns a small shaft that has an eccentric on the end of it. That eccentric sticks out into the exhaust lobe of the crankshaft. The weight it held one way with a spring. So at low speeds the eccentric will open the exhaust valve a little at crank speeds. When the engine hits and comes up to running speed the weight over comes the spring pressure. Then the eccentric is flush with the cam lobe and no longer hits the exhaust valve.
Have you tried a new spark plug. I have a JD pressure washer that has a Honda motor on it. If it starts hard it usually is the spark plug not firing right under compression. Also are you able to crank it good and fast??? As my Dad has gotten older he can't pull the rope fast enought for small engines to start correctly. He complains about this one or that one not starting correctly. Me or my sons can just give it a good yank and the engine starts fine.
I have actually mounted a few snow blower motors on some of the things he uses with a small gas engine on them. The snow blower motors have 110 volt electric start on them. So he can just plug in the cord and hit the button and away he goes.
One of his motors was the same model as one used on snow blowers. I was able to change the flywheel to one that would use the electric starter.