TOPIC:

Ok a bit more info. When I got the bike the previous owner had given up on it because of (you guessed it carb problems) the tank was rusty inside so I chemically and mechanically cleaned it and put a POR15 liner in there. That with an inline filter has sorted the fuel contamination. I checked by draining fuel through the tap and a chemical filter. A mate has one of Scotches cleaning tool which he kindly lent me so the carbs have been cleaned using cellulose thinners with that several times. Spraying aerosol carb cleaner through the various orifices I get a neat jet of cleaner especially through the tiny holes in the Venturi by the butterfly’s. One set of carbs had mullered pilots which I drilled out and replaced with new ones and I’ve done the choke mod so the bike fires up from cold no problem. I thought I had cured it after a 75 mile ride when it ran perfectly from tick over to 70mph (honestly officer) then the following day the problem returned. I’ve filtered and checked the fuel again and it’s still clean. The fuel level is set to 7mm below the float bowl face (manual recommends 6-8 I think. Plus I’ve renewed the plugs twice with NGK BP6ES

I've previously questioned the condition (age) of your idle jets.   Still no mention of them.  If they've been "cleaned" too vigorously with those "wire" jet-cleaners - that could very well be your problem  Two sets of carbs acting-up in the same manner would not be a coincidence if the jets in both have been treated in the same manner. 
In the "79 Carb. rebuild" I showed using the wire cleaners to "clean" jets.  Despite cautioning about their use - something to the affect that we're cleaning and not boring them; I have since posted how destructive they they can be when I discovered and showed the end (magnified) with mushroomed edges - which will ruin a jet. 
I'm getting the feeling that this specific topic is going over the heads of most or simply being discounted as bogus. I guess it depends on your level of patience and how much frustration you're willing to endure.  
 If in doubt about the jet condition - CHANGE them !   If the problems as described continue THEN you can likely relax about it being a carb problem and move on to other areas; such as ignition.  It boils down to a simple  "process of elimination" ! 

Just putting this out-there:  Bad coil, poor electrical connection (corroded), somewhere in the ignition circuit, cross-firing (bad lead). 
Sync. AND ignition-timing slightly off.  This one is easy!  With sync.-gauges installed, Advance and Retard the ignition timing slightly.  You may very well be surprised at this relationship !!!!. 
This will help with a Light-bulb" moment and get you running towards the bike.....and not away from it 

Hi biltonjim , Nothing untoward , nothing to make you listen harder and say '' Hell , whats that ? . From memory , it was more a problem when low revs / low speed , misfire , hesitation , something ''felt '' more than heard  , get on the Throttle , and the Problem appeared to '' mostly '' disappear , and then return when back to low Revs .

A bit off topic, sorry, but I can confirm an exhaust cam 1 tooth advanced won't cause valve clearance issues. DAMHIK?

While waiting for my new Denso plugs to arrive Ive goth the carbs off and on the bench again! Every jet and fuel gallery is clean and flowing aerosol cleaner. However, I’ve noticed that while the slides are free moving in the carb body’s when I couple them up to the diaphragm plate with the diaphragm placed in the carb they tend to hang up even before I put the carb top on? could this be causing my problems? I know the vacuum and suction when the motor is running will move them but with the carbs not having a return spring surely they should drop under their own weight?
Your thoughts please gentlemen 

No idea if that could be your Problem , but doubt it , as you say runs well at higher revs . Here is what I do when fitting Slides and Diaphragms . Holding right and left slide with thumbs and fingers , I carefully slip them into their respective holes , and gently rotate them a little back and forth , just to find that sweet spot . I then check the Diaphragms are seated correctly , with a nice even look to them . When fitting the top  I try the action of the slides , and carefully find the best position for it , then tighten the screws .