Poor spark

Hi All, 
The summer is around the corner in the UK, so I have decided to dust of the KZ1300 and get it ready for a excursion or two. Well that was the plan.
Despite my best efforts , the bike does not like to start. I can get it going using "cold start" but it will not start under normal running, regardless of temperature.
I cannot believe that the problem lies with the carbs, because when it does run, it runs nicely. 
What I have discovered however is blacky sooty sparkplugs on cylinders 1 and 6. Not so much on 2 and 5, which feeds from the same carb, with the same settings.
Now my theory is that I managed to but some crap Chinese knock off plugs, due to them failing quite frequently. These were NGK BP 7ES. I also notice that the spark is very weak. So weak I feel that it is not able to start the bike or run it at low revs. When I take a plug out when the bike is not starting, the plug is wet, so I think it is getting fuel. So here is my question!! . How can I improve the spark? A year or so ago, I replaced the 3 coils, HT leads and plug caps, but yes they were simply bought from a supplier on eBay, suitable for a KZ1300 it stated ! 
Are there better parts to be purchased? Does the issue lie elsewhere perhaps?
Thks
Bruce 
 

I believe the standard plug should be BPR6ES. I run the iridiums in mine though

A BPR6ES spark plug if it is of a good brand can cost between 6 and 8 euros.Much less if it is of Chinese manufacture.

 
 If you decide to install an Iridium spark plug, much more durable and efficient, BPR6EIX.Its cost is between 18 and 25 euros.

 

I have gone the Iridium route, £16 a piece. BPR6EIX.
I once again bought some new cheap plugs, before I realised that they may be the source of the problem. They can now go to landfill !!
I so want to be able to ride this bike with some degree of reliability between my thighs ! It is not a bike to push home !! The small amount of times I have ridden it, has made me realise how nice this bike is. I have never ridden a bike with such a long first gear !! Around the city streets of where I live, you don't need any other gears.