Motorcycle Repair: Piaggio Zip 50cc, air leaks, fuel mixture

Question
hi there, i purchased a 2001 piaggio zip 50cc about two months ago. it worked completely perfect untill a couple of weeks later. i keep getting a spluttering noise when i open it to full throttle and the bike almost stops dead. i have changed the HP leads, cleaned the exhaust, cleaned the carb, placed a second hand automatic choke value onto the bike and still nothing works, have you got any suggestions? please help me.

Answer
Max,

check the color of your spark plug
it will tell you if the fuel
mixture is too much fuel (rich=black)
or too lean (light colored).
Once you know what the engine is
doing you can look for related causes.
Check for air leaks around the carb.