I will not say that you do not have an air leak, but consider the source of the observation; the problem may have another cause. I know there are a few guys at my field who go around diagnosing every issue other flyers have, without even taking a good look/listen at the affected plane or engine. Typically, they have the same answer for everything...

If you have eliminated most possible air leaks, don't rule out the possibility, but look for other causes. A needle setting that is not near optimum could be the culprit as was suggested above, or it is possible there is debris in the needle assembly as well(this is less likely, but still possible). I've had bad fuel cause an engine to run in a very peculiar manner as well, but then again, that was with one particularly ornery old Fox engine...