Shading indicates where throttle lever must be filed to correct fast idle.
When an engine fails to return to a normal idle on a 1958 Mercury equipped with a Ford carburetor, the trouble may be interference between the accelerator rod clip and the throttle lever.
You can make a simple repair by filing stock from part of the throttle lever. use a small round file in the recessed curved area and a small flat file to clear other interferene.
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