drewpy from the UK suggested placing the carbs in the vise and ensuring it was level to set the float height using a manometer. Speedog from Ontario, CA also suggested the plastic-float height should be 22.5mm. (It is possible I got these mixed up, if so I apologize)
I had set up the floats according to the Haynes manual at 32mm, the bike ran badly and was backfiring, found the right carb was flooding so stripped it all down, cleaned everything, checked the needles and seats with a jeweller's loupe to make sure they were perfect. Set the floats height and checked the level, 2mm below float chamber top and whether there was flooding with manometers.
I also installed a shut-off valve between the petcock and the gas inlet because the petcock drips and I can't fix it.
After all that I started the bike on full choke, it revved high as usual but it won't idle so quit for the day.