"Verify the throttle is sitting against the idle stop screw at idle. With engine cold and at idle, push the throttle shaft against the stop screw - the idle speed should not change. Allow the engine to warm up and repeat the test - the engine speed should decrease to 1000 RPM indicating the governor is allowing the throttle to open."
That's a good idea. Would tell you right quick if it's the governor or the carb.
Assuming it's the gov, don't know the solution for that...adjustment, how-where.
If the carb, and the fact that the control is a rigid (adjustable for desired operating rpm) cable, where is the mechanism for the butterflies to open an additional amount, especially for that kind of rpm change.....possibly a weak return spring.....that just dawned on me and may be the culprit and add to the fact that the problem has gotten worse as operating hours have increased on the engine. Engine was bought back around 2006 best I can recall, maybe 600ish hours on it.
Thanks for the input,