Just a guess, but I'd say "gunky main metering needle", getting hung up..... particularly since re-choking it fixes it. If you're familiar with the innards of one of these, disassemble and clean it like you were in a clean room. Don't tweak on things, just clean every passage you can get to thoroughly.

If problem persists - find a REAL "lawn and garden shop" where the guy knows Walbros and give it to him. If not - buy a replacement carb.

Or do a complete rebuild by buying a full rebuild set....but only if you know your way around inside one of these boys.

(Personally - I'd do the clean and replace.... then a new carb.)