Remove the needle valve and then with fuel in the tank, gently blow into the vent line. You should see a stream of fuel come out the needle valve hole with a very slight blow. If it takes any presure, pull the tank and check for a clogged clunk, and for cracked or bad lines. If that seems OK, screw in the needle valve just enough to get a seal with the O ring and again blow into the vent line. You should see fuel exiting the spray bar. Repeat with the idle jet needle. Put the needles back to factory start settings and see if you can get it running then.

If the engine has been setting for a while, it may be a good idea to take the carb off and put it in a small jar of fuel overnight to desolve any varnish built up. I would pull the tank and replace all fuel lines also just as a mater of preventive maintenance.

The fact that it will start and run out the fuel you put in the carb throat indicates a fuel supply problem. It's somewhere between the clunk and the spray bar.

What happens if you hold your finger over the muffler exit and hand crank. Does it draw OK?

Don