Ive got a Hobbico Superstar trainer with a Super Tigre GS-40. I prime it and it starts fine and runs for about 20 sec. and then dies. If i try to restart it it won't start. If i pull off the exhaust hose and blow in the tank it will fire right up again. I pressure tested the tank by blowing in it and pinching both lines then letting go after about 30 seconds and i can hear a puff of air come out so i'm sure it is sealed. I also pulled the exhaust off and cleaned it and made sure everything was clear. Also, when i prime it it will suck fuel up to the carb but it will not stay there. What else could be causing me to lose pressure after running for a while?