Can't start my kz400 1979

Hello, this is my first post here. I bought my kz400 last summer, it has been modified into a scrambler look.
But here is the problem:
It ran perfect last year, put it away for storage during winter in a cold garage and now i am having trouble starting it.

I got it going on idle several times for about 30-40 seconds, when choked the rev rises, but the moment i touch the throttle it stalls.
I pulled the carbs and cleaned the jets and refitted the carbs. Got it started one time with start gas and revved it up with the throttle but then it just stalls again and i cant start it.
Tried all choke settings but it just wont start.

Anyone have any idea?

Also, how do you use the choke lever? Full choke on any startup? And if it has started but stalled, full choke again? Dont know how to use the choke, this is my first old bike.

Hope anyone can contribute with some knowledge because the short summer is passing fast here in Sweden

I'm going to go out on a limb here and say you stored the bike without draining the gas from the carbs. Classic symptoms of a dirty / clogged carb. They need to be cleaned and by cleaning I mean taken apart and the little passageways cleaned along with the jets not just hosed down with cleaner.

Remove petcock and clean the filter mesh and Sediment cup.

No I did not drain them

Which are the "little passageways" and if not cleaned with Cleaner, how should i clean them?

Do i need to remove petcock even though gas is flowing?
Kind regards

The little passageways are going to be most likely in the pilot circuit. Remove the jets and trace the circuit and make sure carb cleaner exits where it should when sprayed in. Basically you should trace every circuit and make sure they are clean.
Be careful with the petcock. Some parts for those KZ400 petcocks are NOLA.