My h9000 is connected to ableton live via usb and I want to send a midi clock from the sequencer via the h9000 midi output,

but my Midi Clock out doesn't work.

The H9000 doesn't currently forward MIDI clock from the USB input to the DIN output.  It's a good idea though.  We had a discussion about this and decided to add a "soft thru" option so that MIDI input from a DAW or USB-connected MIDI controller gets propagated to the MIDI out jack.