Walk Behind Lawn Mowers

I bought HU775H mower last September and used it first time this spring. Few weeks ago I noticed smoke on first start and some gasoline leak. I assumed that there was issue with carburetor and took it to autorized shop for repair. I was told that carburetor was dirty which made valve stay open and pour gas into cylinder. In same time gasoline got mixed with oil. So to clean all that mess costed me $100 and it is NOT covered under warranty.I am really disappointed, so far, at Husqvarna (company with great reputation) and their warranty coverage.
I live in the city and don't have huge yard. I take care of my equpment and bought brand new gasoline canister when I purchased mower.
Any suggestions what can I improve to prevent from spending all that money once or twice a year.

If carburetor is so sensitive is there room for improvement (adding gasoline filter)