Motorcycle Repair: Yamaha big bear 400

Question
What cause it to start back firing and stalling out when it gets up to a certain speed.

Answer
Jason,this is a tricky one. It could be a number of problems. The CDI cold be going out or the pick up coil and stator could be going out. It could be the coil or even the resistor plug cap on the coil wire to the plug. Some of the big bears would even bend the crankshaft key that holds the flywheel in time. Some testing is in order to narrow down the problem. Inspect the spark plug to see if its charred or lightly brown. There could even be a valve clearance problem that they are to tight and don't have enough clearance when they heat up and float out also making it hard to start. Some testing is in order before you spend any money on random repairs. If you can get your hands on a Clymer manual it will help you in testing and narrow down the symptoms.