Hi!
It's easy!
Your description tells me of an engine that has the idle screw turned in too far. Just turn it out some (a quarter to half a turn or so).
The idle screw is blocking the fuel comming into the carb!

Pinching the fuel line isn't a good method to set the idle!!! Rather crude methode.
You have to learn how to set the needles by ear...that way is far more accurate.