running without a screen is risky, now youve told me that and coupled with you tank cleaning escapades...it's a good bet there is crud and rust between the carb spogot and the carb float valve, however to sort this out you would have to remove the carb, remove the float bowl, remove the float, remove the float valve seat (the brass thing) and its gasket...and blow it back with compressed air.
I have witnessed this crud in this place myself