or do what i do and get a short piece of exhaust pipe like 4 inches long that fits the pipe which your air filter goes. weld a flat plate on one end, drill a hole and put a tyre valve in it and youve got your own air leak tester and all you do is remove your air filter and fit it in the pipe then put about a bar of pressure in it and youll very quickly hear the leak and you will find it straight away