Once the bike is running, it seems to rev resonable well, although not a really crisp sound, sounds a bit bogged down, then after a few minutes it cuts out, if I change the plugs it runs again, but the plugs that where in there are all fouled up and the spark doesnt go across the correct point of the plug, it arcs to the side.

I just had a thought.....could is be coked up exhausts or ports? the power valves turn freely so I guess its not the ports(maybe I should check though)...maybe thats something else I could look at.