Leaking air through the nose when drawing chords

Hello David,

I have a problem with Solo Harmonica Study 1, Ex. 2.1, because of air leaking through my nose. I can play only two measures in a row and then I have to exhale. If I close my nose with my fingers, I can play 4 measures and even more easily.

I have read all your tips on closing the nose here in the forum, but nothing works for me when drawing more consecutive chords like in this piece. Would you advice an exercise to address and practice this particular problem?

Thank you very much,

Marek