If it's a needle adjustment that is needed, it's most likely the low speed that needs to be leaned a little.

Here's a couple of links that will help to walk you through it (Yes they are fom another engine brand but the information remains the same)

this one is direct from the Walbro book

[link]http://www.zrcgf.com/pages/files/Tuning%20A%20Walbro%20Carb.pdf[/link]

This one is about running in bit it simplifies the tuning procedure

[link]http://www.zrcgf.com/pages/files/Master%20Series%20-%202%20Stroke%20Engine%20Break%20In%20Technique.pd f[/link]