Sorry to hear about this bad GMS experience. On my side of the swamp these engines are very popular. Between us we have approx 5 or 6 of these engines in a variety of airplanes. I remember that one was hard to get going reliably at first, but now they are all great. As for the airleak issue, the ones we have here ALL must have leaks because they are hard to shut down will the throttle closed. But in spite of that they scream at full throttle , the transition is great on all of them and they just won't quit at idle. Is the carb clean ? Is all well in the tank plumbing ? Try a different glowplug. Maybe your engine was made late on a Friday afternoon. Contact your engine supplier. As for the Tower Hobbies 46 BB - I have only one - with the rear needle valve, it is mounted inverted in a Tower Voyager and it is a great little powerplant.