Atul's method will work. The other thing that is important is to let the engine cool 15-20 minutes at least between flights. The engine does not like to start when hot. Your 600mah battery should be more than enough as I'm drawing only 160mah per flight directly through my receiver including all my servos on a 10 minute flight.

How long are you letting the engine sit between flights? Sounds to me like it is just hot,

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