A neighbor was sorting an older Craftsman brand mower with Kohler engine. There’s a linkage between the business end of the engine and carburetor. I figure it’s for the engine to manipulate throttle since the carburetor has no means to move the linkage other than relaying throttle position. Engine speed changed rhythmically as the linkage oscillated. Is this normal or is something wrong? It can’t be normal for idle to pulse like that. What’s the purpose of that linkage?

Sixto
05 E320 wagon 173K miles