The PA50 has a reed valve under the carb. Did you check to make sure the reed valve is opening and not stick shut by old varnish?
PITA to take it off again I know so start at the tank and petcock and make sure you have fuel flow into the carb. I think the petcock has a filter at the bottom that can be removed and cleaned.
You can open the drain on the float bowl to see if it is filling up.
If you have fuel flow, then you'll have to remove the carb again to check the reed valve