Just bought this TW200. 340lb. rider. Upsized the rear sprocket to 55. Warm engine, Feathering the clutch while trail riding causes a loud chatter with shudder and slipping under partial engagement while moving ahead from a stop or low speed. Thought it might be wrong oil used by previous owner. Drained oil looked clean, not burnt. Refilled with silkolene pro 4 10w40. Havent had a chance to try it. Return spring OK and adjusted. Basically shudders at engagement.