I do all the things Fizz listed to the new engines, as well as remove the spring that pushes the carburetor barrel out. The barrel sometimes loosens and this spring will get ingested into the engine and it is toast (I know first hand!). All you have to do is loosen the barrel retaining screw, pull out the barrel and the spring (throw away the spring!) and put it back together with locktite on the retaining screw. You can replace the spring with a 3/32" slice of fuel tubing, but I have never worried about it. You will start and fly at full throttle, and only use the throttle to cut the engine off. The barrel retaining screw will keep it in place.

Best wishes,