I had bad starting problem and running until warm on a 2 year old XJ6 I had while working in Southern Germany.
I constantly looked like the third starting carb. Tried lots of things over some time but could not get 'good starting and running'. I even put a new unit on. I ended up taking the third carb off and blanking the hole.
The car would then start no problem in minus 10 deg by fanning the throttle when starting it. Once it started it needed just a little help fanning the throttle for the first minute to pull away. I never bothered to put it back on. It made not difference in normal temperatures.