those "white fuzz" from pot-metal corrosion is caused by moisture-induced deteriorated gasoline soaking the pot-metal (primary material of choice for making carb).
I've been using B&S advanced fuel treatment to dope my gasoline for OPE for the past year now, and I'm putting my faith on the additional metal deactivators and anti-oxidants that came along with it to protect my B&S mower carb from deterioration.
I don't believe in firing up OPE engines once a month , for once I properly prepared my OPE engines, they will be prepped and stored (esp. in the case of my 2 recently acquired prized Honda portable gennys) for a few years at a time, and then will be fueled and fired up when they are being called for.
For Honda OPE engines: I'd drain the carb before fogging the engine; for B&S sidedraft with walbro clones, I shut off the fuel supply (gasoline doped of course); run and fog the engine before putting it into storage.
those metal deactivators will keep my carb in good state over winter time.
Lastly: unlike most OPE users: I'm never afraid to tear any carbs apart and investigate (rebuild them when needed), so, to me, carb problem may never be an issue afterall.
Q.