that depends, if the spark plug is fouled or not, connections from the ht lead but it could also be compression issues or a simple case of valve clearances. i would personally check the valves first, they should be set at 0.04mm do this first and see how you go, usually any loss of power is from incorectly set valves its the most common thing around. so get those checked out, if you still have problems then you might want to check your plug and/or do a compression test. not really alot more i can say.....have you rejetted the carb just out of curiosity? because i assume you have derestricted it. anyway sorry im rambling hope you get it sorted
safe riding
