As the title says, hollow brass floats get pinholes in them and....well, sink. But in addition to your new parts, this is what I would do. It has worked 5 out of 5 times recently on outboards and lawnmower engines.

Disassemble the carb completely and remove all screw needles like the idle screw and any jets that have a slot in them. Use a correct size screw driver to remove. The purpose is to expose everything to the cleaning solution.

Then buy a gallon of carburetor cleaner at your local auto parts store. Dump the parts in and let sit for several hours. Turn them over and let them sit another few hours. Reassemble the carb. A good starting point for needle screws is 1-1/2 turns out from closed.

I'll bet it will start and idle smooth after that treatment.

David