Progress so far...

Can I suggest taking the carbs off the bike and setting them up level on the bench with your bench fuel feed connected. Not to check the levels but to check that carb 3 isn't flooding after a couple of minutes. I say this as I'm having trouble with mine.  It runs fine every time I start it up in the garage but it turns to crap after a couple of minutes test drive.

I took my carbs off to check the levels and they were all as expected.  I only noticed the flooding because I forgot to turn off my fuel supply. I've replaced all float valves with originals with new viton O-rings but I just cannot get the left hand carb to stop flooding. This is only with the weight of a few 100ml of fuel too. Have a couple of very expensive originals coming from our friend Helmut in Germany - I couldn't afford 3!

Thanks Stocktoy, good idea, I might pop past the paint surpliiers again first, in case I can speak to a more senior person who might remember Cellulose thinners. as the guy I asked there was quite young (well cellulose thinners isn't an app )...worth a try.

Thanks zed-thirteen, as the carbs have to come back off that could be worth checking out, especially as the fuel petcock doesn't fully shut off. It weeps very slowly I tried the polishing compound trick but I probably wasn't agressive enough as I didn't want to over lap it. I'll have another go at that.
I also replaced the float valve o-rings with viton. I replaced one of the float valves too, from Helmut, but not with an original...yes they are a little pricey . I buggered up the original float valve as I couldn't get it out, hopefully not because of the viton o-ring...not my finest hour. . It was a tight fit...
Now that's got me trying to remember which carb body had the new float valve...


 

www.kz1300.com/index.php/forum/carburato...rb-rebuild-pt-1#5423

and use some silicone grease on these orings

Further to the problems: Flooding with new float valves could be an indication that the OEM Nitrophyl floats, are breaking down and absorbing fuel. A "dry" OEM float will weigh 10.7 grams +/- 2 grams. Put your floats in a container of fuel for several days and weigh. If after "soaking" they weigh more then 11.5 grams - your floats are questionable.
If you have backed off the sync-adjusters to avoid binding and the idle is still slow to return or otherwise erratic, it is an indication that the Choke Fast-Idle adjustment is incorrect. The "roller" can not touch the fast-idle Cam when the choke is OFF.
www.kz1300.com/index.php/forum/carburato...-days?start=12#17477

Ok thanks Scotch. I'll do all of that and see what the results are. I only replaced one of the float valves but I'll chack that.
I didn't back off the sync adjusters in the end as they felt ok to me. There wasn't any play exactly, but there was free movement as I rotated them.
The fast idle cam does need adjusting for sure now as I re adjusted it as a last resort when all else was failing.
I finally managed to get hold of some Cellulose thinner today also, so hopefully I can get to the bottom of this soon.
 

I finally got round to pulling the carbs back off and stripped the number 5-6 carb with the cool pipes...cool in the temperature sense .

There is another common denominator, this was the carb which has the non original Kawasaki replacement float valve. Hmmm could it be the issue? I hope not, the Kawasaki ones are  fffff er very expensive...