carburetor

I have a Hyundai 510sp lawnmower that is surging and I can't figure out what's wrong. I've cleaned the carburettor about 5 times with carburettor spray and enlarged the 2 valves slightly with a micro drill bit. All the little holes are clear. It was fine last year but I did leave fuel in it over...

Got a mower with Brigg Stratton Quantum xm50 which smoke black and won't rev. I cleaned up the carburetor but nothing had changed.