Lawnmower Needs Work—Carburetor?

[mrlynn]

My little 22" push Poulan was running rough at the end of the season last year. Now that the grass is (finally!) starting to grow, I started my regular beginning-of-season prep: sharpen blade, clean air filter sponge, change oil, and new spark plug. I pulled the plug, and see that it's black with carbon. So it was running rich, I think. This is a Briggs and Stratton 500-series engine. I don't think there are any adjustments on the carburetor (these new-fangled, regulated engines don't even have a throttle!), so I assume it's either take it apart and clean it, or just get a replacement. Are they available?

Or could it be valves?

Advice welcome.

/Mr Lynn