I am a p-51 fan and had to buy the mustang but now the engine isn't running right! After first flight the engine sputters when going from low to high. After having one flight every one, including some guys wife, mess with the engine I packed it in the car and went home. The next day changed glow plugs and with new fuel I noticed air bubbles in the line so I changed all the lines thinking I had a pin hole but no luck. Please any one why do I have air bubbles?