Low speed needle is too rich. Look at the carb, it should have two needles. Near the base of each needle, you should see an "L" and an "H" cast into the carb body. These walbro carbs are very touchy, so it wont take much. Turn the one with the "L" in about 10 degrees to the right. That should fix it. If the engine is old, and has a lot of hours, the spark arrester in the muffler could be clogged (coked), your engine may not have one... but its usually a little screen between the engine and the muffler. Remove the muffler and you should see it, then throw the screen away, its only needed to pass EPA crap. This is probably not the problem, but couldn't hurt to try. Don't take the carb apart until you are sure you need to, you WILL tear old gaskets. If you do, plan on buying a rebuild kit (not a bad idea in the first place).

I used to work at a small engine repair place when I was in High school, man I miss playing around with them.