This can happen ,its rare and loctite would be the insurance for it not to happen, and yes the meatal is weak so the backing plate screws are easy to strip if you over tighten , I always use blue loctite when assembling the aircleaner backing plate to the carb , The S&S /zenith/bendix carb body assemblys is designed with the screws inside the filter diameter to secure the backing plate , So I am assuming your carbuerator was one of the 3 mentioned above. I assume youve done some good top end damage , Well look at it as a excuse to do a nice big inch build on your bike .