Try this directly from the Walbro serivice manual. Squirt fuel into the spark plug hole and try to start the engine. If the engine fires then you have good spark and compression for the engine. Next try squirting fuel into the carb throat if it fires the problem is most likely in the carb or fuel system. Here is a link to the manual. Page 9 and 10 of the manual is where you need to look. Keep us posted. This is a PDF file so you can save it to your drive for the future.

Walbro Service Manual (PDF 5.8MB) http://www.wind-drifter.com/technica...viceManual.pdf

This link has some interesting ideas regarding midrange RPM

http://www.geocities.com/farellus/idle_adaptation.html