Hi Trevor, welcome to Outdoorking. Please post the full set of numbers (Model, Type and Code) that are stamped on your engine's cooling air cowl, plus a picture of your governor's external connections (remove your air filter and photograph the linkage that connects to your carburetor).

The owner manual for your mower is available in the manuals section of this site - subscription is required. Here are a couple of illustrations from it, relating to your mower.

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As you can see, the Pro 12, unlike the Pro 16, has the choke connected to the speed control linkage, so the choke is automatically applied when you advance the speed control to the extreme position.

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This is the carburetor for your mower. It is called a Large One-Piece Flo-Jet.

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Here are the instructions for setting up the linkage for your speed control and coupled choke. Personally I find them indecipherable without photographs of your actual linkage, which presumably has been "improved" by the previous tenant. That is the area I want you to post photographs of.