An airleak means that air is accessing the engine at wrong places. (Through the front or back of the engine (engine bearings) or between the carb.)
You will have to seal the engine. A guy named Squirrel on YouTube has a how-to video on this subject.
http://www.youtube.com/watch?v=6xwDy-I0Z4I
Take a note on that you need gasket material (used for sealing with). He recommends using gasket material that can withstand enough heat just in case. With this gasket material you can seal the backplate and the carb of the engine. Next up is the Team Associated's Green Slime which he mentions also in the video. Use that to seal the Low Speed Needle (LSN) and the High Speed Needle (HSN), he shows you also how to do that.
Good luck!