I had a Poulan saw that did the same thing and it ended up being the fuel hoses ,it had too tight of a bend in the hose ,worked fine when I first put the carby on then a week later the hose just would not let enough fuel through with a slight bend must be because the lines are tiny inside.
Also if you get this problem I reverse the fuel lines just to check ,sometimes you can mix them up and sometimes running the lines in reverse, then if that doesn't work put them back on the right way and it has cleared the problem. Probably gets the one way valve working for the primer also you will test the valve by it working one way and not the other way.
When the primer bubble (purge bulb) has a problem it could cause this problem if the one way valve isn't working ,I also reverse the lines on the primer if it's a remote primer and try it both ways as that can sometimes get the one way valve working again and you will see if the one way valve is stuck open as the lines should only work one way for priming.
Try it with a fuel filter that you know works fine and sometimes you can get a slight leak in the fuel hose inside the tank above the fuel level.Replace all the hoses as second hand hoses are very dodgy but you've probably done that already.
