Carb problem

yes the plug should be a nice brown colour if the bike is running well

Back in the day when cars had carbs I used Gunsons Colortune plugs to set the mixture.

Gunson Website

Funny enough I bought a Gunson Colourtune in the week and tried it out on one of my other bikes first and it is a very good piece of kit and gives you a very good idea of what is going on.
I then tried it on my CB 500 and I am 3 turns out on the left hand cylinder and 1 1/4 on the right. So the puzzling thing is why am I still nearly 2 turns out than the other cylinder. The same size pilot jet, no leaks anywhere and everything has been cleaned and blown out. 
If I put the next size pilot jet in the left carb that should then bring the air mixture screw between 1-2 turns out.
Any thoughts anybody on this?

I wander if you have an air leak somewhere.  From experience with other bikes, if you have a leaking carb rubber (or similar) it really make adjusting the carbs difficult, if not impossible.  It certainly stops things making sense...

Funny you should post this one, as I checked the bike when it was running and sprayed some brake cleaner around the inlet rubbers air box end and they were leaking and I may have another leak on the side of the carb. 
Are there any o'rings on the butterfly shafts towards the outside of the carb on both sides? The screws on the butterfly's are very tight and I don't want mince them up. I would think there would be some o'rings in there but Honda parts list doesn't show any o'rings there.
I have taken the carbs apart to replace everything that needs replacing.
The parts I need are inlet rubbers, two o'ring for the breather tube and maybe two butterfly shaft o'rings. If it comes to it I will drill out the screws holding the butterfly's on.

There's no 'O' rings on the butterfly shaft.

Good news there are no o'rings on the butterfly shafts. Waiting for the breather tube and fuel feed tube o'rings from Japan to arrive and can then put the carb back together. I will post a reply to how things go.

Put the carb back in again and still running lean on left cylinder. I then replaced carb rubbers both ends and still the same.
What I am thinking now, as I have done everything to do with the carb side of things and the only thing I can think that maybe causing this problem would be the exhaust valves maybe leaking.

A compression check would be the next step I guess.