Demon Carburetor issue

If the carb has never been apart...
1. Take a vacuum reading in gear at idle, and diving around at light throttle. You need to know what vacuum the power valve is feeling in real driving situations.
2. Take it apart and clean it very carefully. Make sure you remove air bleeds and jets, shine a light down the passages, and verify there are no "hanging chads" from the machining of the metering blocks. Make sure you use brake clean and shop air to blow out those passages and the tiny holes.
3. Install a power valve that is lower than the idle level by 1 number or so. Reassemble, reinstall. Test drive it preferably with that vacuum gage again. see what it's doing and if it's still doing it.

It sounds lean to me too, but not the accelerator circuit - the power valve or air bleeds may be incorrect or have "stuff" in them. I have yet to see a brand new Demon that didn't get shipped with aluminum chips and gunk in it and I've had a couple that had machining flash left partially blocking a passage in the metering block(s). That's why I just don't recommend or use them if possible. But you got it - it's a decent design - so I'd try and work with it.