HAD the same problem
wrap some GAS grade teflon tape around the intake BEING CAREFUL not to get it into the manifold. then put the carb on. it should be a tight fit.
CLEAN THE MANIFOLD REALLY GOOD and sand it do its not so slippery, then put a few wraps of electrical tape around it. NOT DUCT TAPE. im talking about the little black roll that is about a half inch wide. This is what i did and it fixed my problem in no time!