I am new to this forum I have been doing a lot of reading but this is my first post. I bought A friends 2000 scrambler 500 4×4. he told me that he had the stator and pull start cover replaced then after that it would back fire alot. It has sat for about 5-6 years in his shed then I bought it. I replaced the battery rebuilt the carb and cleaned the whole bike. Now it starts right up runs for about 2-3 minutes this slows down and shuts off. I pull the plug and its fouled its not a wet black just a black soot. don’t know were to go next. Any help would be great.