Hello Amir,
On the first stage of the carburator, a choke module (aluminium box) is fixed with 3 screws.
In this box, a small rubber part is mounted, that has hardened over the years (because it is
not resistant to fueldamp). This rubber allows the choke valve to open a little in the first
minute after starting the engine.
Years ago I had the same problem and had to find out what caused the problem. It appeared
that the rubber part in the choke module, had hardened.
To find that rubber, you have to remove 4 screws on the back of the choke module. In this
rubber a piece of steel is mounted, as shown on the foto underneath the choke module, which
you have to remove and fix to the new fresh cut rubber part.
If you cannot obtain/find the rubber, I can help you with this part.
By experience I can tell you, that this treatment of your choke module, is the solution.
Good luck with the job.
Best regards,
Paull