Thanks for all the replies, these are the findings:
First I removed the float bowls, turned the petcocks to reserve... a few drips came out both sides, no sign of water in the bowls.
Tried the same with the fuel lines disconnected from the tank, only got drips out of the petcocks.
Stripped the petcocks out both sides.
Let gas run out of each side into a clean receptacle, there were a few paint flakes, no water.
PO had repainetd the tank at some point, when I first got the bike there were flakes of paint in the tank, obviously needs coating inside which I will do later (need to use the bike now!)
Pulled the sleeves off the petcocks, there were more paint flakes on the outside & inside of the sleeve, cleaned and blew back through the valves, all looked good. Note there was no obvious blockage, there was 95% of the screen clear of any debris.
Re-assembled and gas ran cleanly out of both sides.
Re-assembled to bike, still no gas out of the float chambers!
When I overhauled the carbs I replaced the fuel lines and in line filters, less than 1000kms ago, yes, the filters are pointing in the correct direction.
Progressively removed portions of the fuel line and the filters were blocked! Blew through them (by mouth) and they were miraculously cleared, now everything works perfectly.
So, it appears that the blockages of both the petcock screens and the fuel filters is by some very small (invisible) particle which is readlily displaced with a bit of pressure ie: blowing by mouth.
That's a bit of a new one for me (is it a contamination in the fuel?), anyone had this occur before?
Orange...cause it makes me look like I know what I'm doing!