While I don't have a Matrix, I do have a Nemesis. Should be not air bubbles in the fuel line. When I got my Nemesis it had the same problem, air in the fuel line. I replaced all lines, fuel and pressure line, and haven't had this problem since. The low speed needle is the one on the carb slide. Right where the serve pulls open the throttle. The high speed needle is right next to where the fuel line enters the carb. Not sure if this is exactly the same on the Matrix, but most carbs are like this. Not sure about the break in positions. On the servo twitch, they should not twitch with the motor off, or on. Try setting the trim on the transmitter. Also check the end-point adjustments, as you don't want the servo constantly tugging on the linkage when the throttle slide, brake, etc. is already open all the way. Hope this helps. Let me know if you have more questions. I'm fairly new to this stuff also, but learning very quickly.