My Deere L120 runs full throttle -- think I've incorrectly attached throttle cable

[deerel120]

The throttle should always be open fully when the engine is turned off regardless of what position the throttle lever is in because the governor spring is stronger than the throttle spring.
When you move the throttle control, the wire turns that plate.
The plate stretches a spring between it and the GOVERNOR ARM the governor arm should be the only thing connected to the throttle butterfly and that has to be a solid rod.
The spring pulls the governor shaft into the open position.
The engine rotating mover the governor into the closed position.
When the engine is stationary the governor holds the throttle wide open
As soon as the engine starts to turn the governor closes the throttle down to whatever position you have set the throttle control to.

Put your finger on the governor lever, you should be able to move it by hand to fully close the throttle butterfly.

And remember the throttle butterfly is the one that you can not see at the back of the carb nearest the engine.
The butterfly at the front is the choke.

People not familiar with these engines get them confused and on some engines you can transpose the control cables

Bertsmobile:
With the insight from your message (above) and watching a couple of Youtube videos on governor adjustment, I finally figured out the problem. The shaft to which the governor arm on my machine is attached needs to be turned counterclockwise on my vtwin. Seems like every other machine in any video I watched is set when rotated clockwise. I finally was able to put the puzzle together when I saw a video with someone in the crankcase demonstrating how the governor actually works and then I understood that mine had probably needed to be adjusted forever because I never really did have much throttle control. And now I do.

What tipped me off was the fact that rotating the swivel plate wasn't doing anything to slow down the engine and there wasn't any play when I -- as you said above -- "put your finger on the governor lever, you should be able to move it by hand to fully close the throttle butterfly." Another Youtube video demonstrated the operation of the swivel plate and showed that when the throttle cable moves the plate to throttle-up the machine it stretches the spring between the swivel plate and the governor arm -- but the way mine was adjusted the spring had no tension at what I thought was wide open throttle -- so I figured things were backwards; it all worked when I made the governor adjustment you would make for a governor shaft that is rotated counterclockwise to set.

I'm still not out of the woods, though, because when I put the new air filter on it (brand new air filter) it started running rich and bogging down. Took the air filter off and the engine worked like a dream. Not quite sure why that is, It wasn't dusty today so I went ahead and mowed. Had to. But any thoughts about why putting the air filter on would make it start running rich?

Thanks for your help.

 

[bertsmobile1]

Congratulations,
I hope you have gained some satisfaction from finally nutting out a problem you seem to have inherited.

I cop a bit of grief for the lengths of my posts but I have always believed in the teach a man to fish philosophy.
Once people understand how things are supposed to work , most can nut it out, mowers are not rocket science.

To burn properly you need a specific ratio of air to fuel.
Air filters reduce the air flow so if you are running rich with the filter on and running clean with the filter off, that says you are getting too much fuel.
The engine breather can also cause similar symptoms so the first test is to disconnect the tube that goes from the engine to the carb don't pinch it off, just pull it off the carb end.
If that makes no difference then the main jet is too big , missing or not seated properly.
or the level of the fuel in the float bowl is too high.