Verify that the throttle cable is actuating the accelerator plate through the links. These can sometimes be caught or obstructed by small grass or twigs.
Make sure the governor's linkage does not keep the throttle closed. A governor is a device that regulates the speed of an engine, keeping it constant regardless of the load on the engine. On a lawn mower, two types of governor are used. A system consists of a paddle pivoted at one end and connected to the accelerator plate in the carburetor through a spring and joints. The air is directed from the flaps of the steering wheel to the fin. If the motor slows down (due to long grass), this reduces the air force on the paddle. This allows a spring to open more the throttle, allowing more fuel in the engine, which gives it more power and this increases the speed to compensate. The governor also limits the engine's excess acceleration by closing the throttle when the load is reduced. Another type of governor works by centrifugal force. A spool that can slide on a shaft acts on arms that move more outward as the engine speed increases. The Reel powers the accelerator through links.
With the air filter removed and the use of a torch, you can determine the position of the choke and choke valves. These are dishes that open or close at the entrance. The outermost plate is the choke that almost completely obstructs the airway when it is turned on during a cold start of the engine. The accelerator plate creates the slightest obstruction with the throttle thoroughly and the regulator binding should not be closed before the engine starts. Verify that the governor can move freely and does not stick.
