luvpsi, none of your pictures shows the area around the idle discharge holes in the carburetor bore near the throttle plate. Here is the idle system explanation from the Walbro Service Manual, Page 7. I have circled the bits you are interested in, in yellow:

[Linked Image]

If you can remove the adjustable idle screw and squirt carb cleaner into the hole it comes from, you should find the cleaner blasts out through the three holes just before and after the throttle butterfly plate. Hopefully it is not necessary to interfere with the adjacent metering chamber, because the engine runs properly off-idle and at higher speeds and loads: the problem is likely to be in the idle pocket and the area immediately around it.

Carburetors are "flowed" at the factory to match a standard air fuel ratio profile across the operating range. Mixture controls are adjusted to align closely with the profile, then sealed. There is no attempt to adjust mixture after attaching the carburetor to the engine. Hence if you fit a carburetor intended for the same engine size and type, it should be fine. Subject to emissions control regulations, later service adjustments may be either easy or difficult.

In case it makes useful light reading, here is the full Walbro Service Manual:
http://wem.walbro.com/distributors/servicemanuals/ServiceManual.pdf

Last edited by grumpy; 17/01/13 03:24 AM. Reason: Add detail