Fuel not going into the carburetor

[Gustaf]

I can only get my GZ250 started if I put the fuel switch into PRI position for at least 5 seconds.

Then it runs for a couple of minutes, starts sputtering, and stops. It will not get started unless I put it into PRI again.

My motorcycle has been in storage for a while, but I was able to get it started without any problems a couple of months ago.

I added new fuel, the engine sounds better now, but the problem persists.

Any suggestions will be much appreciated.

Thank you,
Gustaf