Number 4 cylinder

Hi
my 1978 Z650 B2 starts easily enough but the right hand (no4) cylinder does not get hot for about 3 or 4 minutes, when the other Dow pipes are very hot it is still cold to the touch, after a short while it gets hot and the bike seems to run normally, I have taken the carbs off , stripped and cleaned them which cured an initial start up issue but it is still slower to reach temp than the other 3 cylinders, any suggestions what to try checking greatly appreciated.
thanks 

If the pilot jet on that cylinder is definately not blocked or partially blocked i would be looking at the plug on #4 prior to first start up for signs of wet oil fouling.
There's a chance you have a leaking valve stem oil seal which will allow oil to weep down the valve stem overnight and wet the plug which will then take a while to clear on start up.
A clue to this is that once started the bike will usually behave fine the rest of the day and the problem will only again re-occur when the bike has been stood overnight.
There are other issues that may cause the same symptoms such as a faulty plug or lead etc but the oil fouling is the more likely suspect once the carbs have been ruled out.

Sounds like you need to clean the carbs better.  

Did you remove the pilot jets and hold them up to a light to make sure the passage is open?

Remove the choke plungers, squirt carb spray through the small hole in the bottom of the passage, and confirm it comes out from the choke pick-up tube on the bottom of the carb?

Spray carb spray through the choke pickup fuel passage in the float bowls and make sure the passage is open?

Did you remove the pilot jet and pilot screw, and shoot carb spray through the passages in order to make sure everything is open?

Is the airbox installed and well sealed?

Did you replace the carb boots on the head or at least make sure they are soft and pliable and not prone to leaks?

Sorry to barrage you with questions, but all these things will affect how well your bike runs.

Good luck

Switch off fuel a couple of min before stopping the bike for the day, does it cure it on start up after switching on fuel? Double check fuel level on the carb associated with that cylinder, check also the needle float valve is sealing properly. 

Thanks that’s interesting because it does tend to smoke a little bit until it’s running ok 

I did clean them but must be honest didn’t remove the choke plungers, the air box seemed ok but the rubbers are a bit hard 
cheers