Drain the carb bowl or turn the fuel off and run it dry. This is what two dirt bikes carbs I cleaned up the other day.
Completely plugged main jet.
The after picture. I took everything apart, soaked it in Chem-Dip, washed it in hot water, and blew it dry with compressed air.
The other was one was just as nasty.
Partially plugged main jet
Plugged idle jet. I didn't get an after picture, but this carb cleaned up nicely, too.