You have a bit of buildup of old oil. Maybe a little dust and dirt thrown in. You could take the carb off the engine and put it in a jar of alcohol, the hardware store type, not the drug store stuff, and let it set for a few days, wiggiling things every day. THis will desolve most of the gunk. Then dump that alcohol and put in glow fuel and slosh it around and work the carb some to get it through out the carb. Wipe it down and re-install it on the engine. If it is realy brown and built up, dismanteling the carb and cleaning it is a good move. I would pickup a set of Orings and replace the old ones, and whether you pull or dismantel the carb, replace the carb to crank O ring.

Don