Old threads with no resolution !
I have same engine and we cleaned out the carb before test running.
Acceleration and speed were low, for a 250 so we looked and noted the slide would not lift, when opening the throttle.
Tracing the path, we discovered, and removed, a rather stiff coil spring which held the diaphragm activated vacuum port.
This is behind a 3 screw cover on the side of the carb. There are other parts that will fall out when the cover is removed, including the diaphragm, a check ball, and an O-ring.
Acceleration and speed doubled, yet we've lost smooth idle, which will probably require adjustment.
I may check the hardware store for a lighter spring... it's about 3x diameter of a ballpoint pen spring and the same length, yet exerts quite a bit of pressure when compressed within it's shallow housing by the cover. We can not imagine the level of vacuum overcoming that spring to open the valve, and in turn raise the slide for more power.
Here on the left coast the State regulators frequently require companies to install 'limiters' on many small engines and we suspect the stiffness of that spring has something to do with that sort of sculduggery.
I will post final resolution to the problem, as we see it, when certain.
redk
