I believe you have more than one issue here.
Firstly the starting.
I have had this issue. In my case it happened mainly when the bike had been stood for a period of time. All the models after the G have vacuum petrol taps and (with exception of the K models) they only have a side stand. This means that with the bike leaning on the stand the fuel will always run to the left. The fuel level will drop as it evaporates but with it being a vac tap it will not get topped up therefore when you start the bike you are doing it with one empty carb which can only fill in spirts as the engine runs. If the bike has been standing you should turn the tap to the PRI position for a couple of minutes before starting. This is PRIME and bypasses the vacuum system allowing the fuel to free flow and fill both carb bowls.
With regards to running only on choke this would suggest fuel starvation and that could be several things. I would highly recommend a full strip down and clean of the carbs and components. Make sure all the passage ways are completely free. Check the carb rubbers (in and out) are in good order and not perished. Check they are fitted correctly and there are no leaks. Check the air filter is clean and finally check the diaphram’s for being perished or holed.
Once all this is done the carb need to be set up and tweaked as required including balancing. The float levels are quite critical but if near enough they shouldn’t cause the problems you are describing.
I hope this is of help.