it could be a bad connection or a faulty starter relay. to rule out a bad connection try putting the bike in neutral, turn the key on and cross the two big terminals on the starter relay with a screwdriver or thick wire. the starter motor should turn the engine over at a normal speed. if it does then all the high current connections are good and it points to a faulty starter relay. if the engine still doesn't turn over with the starter relay crossed, there is probably a poor connection in the high current starter motor circuit. a poor connection could be at the battery terminals, the ground between the battery and frame, the ground between the engine and battery/frame, the 12V connection going to the starter motor or the high current connections at the starter relay. be careful when crossing the starter relay it can cause sparking or you could burn yourself because a lot of current will flow. if you're not sure have a look on youtube for motorbike starter relay bypass, there should be plenty of videos on it.