you know chopper, i had a similar problem as you, it was on a 4 stroke motor for a 600watt generator. I removed and sprayed carb cleaner and i thought it was completly cleaned out. So I reinstalled the carb and still the same results, the engine would only run when I sprayed starter fluid in the carb.
So i removed the carb again , this time I unscrewed the jets and pushed a small wire cleaner thru it that I use for cleaning torch tips. Then I reinstalled carb and the engine fired right up.
Try again with removing your carb and cleaning the jets , you should be able to see daylight thru them, if not then they are dirty.
Hope this helps,I just know it worked for me.
the picture is an example of what a jet looks like
here is also a video example on how to clean a jet ,but its for a snowblower but it what Im talking about
http://www.youtube.com/watch?v=HjzasttXpMU