914 Won't Start Properly When Cold

I have a 912 and was having similar problems. It turned out I had a torn rubber boot on the carb to the intake manifold. It was less than 25 hours since I had replaced the other torn one. Seems to suck together when running so one it starts it ran fine. My Rotax guy thought my thick stiff throttle cables were causing it so we swapped out for lighter ones with some slack for vibration. So far so good. 

Watched the Video.
It STARTS very guickly.
What it does Not do is keep RUNNING.
I would suspect the issue is Fuel related and not Electrical.

What fuel are you using?  Mogas?  100LL?
In the US we have what is commonly refered to as "Winter" Gas. 
It has more volatile components that vaporize at lower temps, making cold starts easier.
Once the intake manifolds warm up, the fuel is no longer critical.

Doug Fox:  How would your throttle cables be causing your carb socket to tear?  That's a pretty thick piece of rubber!  Is it the only thing holding your carb on besides the cables?

Don't think it's that as we had a good look when we changed the carbs

My gut feel was it's fuel, but now we changed the carbs I'm not so sure. We're using UL91 which is unleaded Avgas available in Europe. The engine we had before this one did not have this problem with the same fuel and the carbs we just installed came from it too - it's a real mystery !

Mark