I picked up my bike about 2 weeks ago from my mechanic. The bike started with ease, but after 200 to 300 km of riding the engine sputter. Upon removing the spark plugs, I noticed the plug for the forward cylinder was coated with carbon and wet. The plug on the rear cylinder was also badly coated but dry. Is this due to incorrect tuning of the carb? If so, how do I do the calibration my self. Any diagram will be most helpful.