Check your primer bulb on your gas line. Sometimes the check valve (ball) inside the bulb gets stuck or varnished over and won't hold pressure. It can also have a crack in the bulb that is sucking air. Does the bulb pump up hard? (no smart comments please) Also, if your motor went to half throttle, you may be possibly overheating or low on oil. Some motors have this saftey feature on them. If you tell us what kind of motor you have then maybe we can help you a little more.