First, check the screen on the muffler where the exhaust exits. If that screen carbons over, the symptoms will mimmick what your mentioning.
Here is a link to the Walbro WYK-186 schematic;
http://wem.walbro.com/distributors/servicemanuals/WYKseries.pdf
Notice item #13 on page one of the schematic.
The carb has adjustments just like any other, theyre just in different places. Most of the time the only place that needs attention is the main needle under the plug which is #13. The fuel adjustment needle travels down thru the barrel (page one, item 10). Look at the walbro drawing on the next page down and notice the needle (#2, page two) running down through the barrel.
The plug covers the needle, remove it with a drywall screw or pry it out. You will need a tiny flat blade screw driver to adjust the needle. Counterclock wise adds fuel. Some of these carbs also have a small lock ring on top to prevent the needle from turning from vibration.
If you have ever adjusted a lawnboy altitude adjustment needle valve carb you will understand immediately.
Replace the fuel filter, fuel lines and carb diaphragms while you have it apart so you wont have to monkey with it again in 6 months..