[Harp-L] New chromatic help

[David Smith <dustydave38@xxxxxxxxxxx>]

Happy New Year to all you harpers out there.

I got my first chromatic for Christmas; a Hohner CX12. I am having  
trouble with draw 8 and 9.
Using my usual tongue blocking technique, I can't get any sound out  
of them. If I use a pucker
embouchure, I can get some sound out of them, but not as loud as I  
think they should be. I'm
thinking the difference is the variation in air flow between the two  
techniques.

Is this something that can be easily fixed by myself, or should I  
send the harp back for replacement?

Thanks for any advice.
Dusty Dave