I am battling the same condition on a B&S 12.5hp 286700 series engine. The throttle butterfly doesn't close all the way. I have cleaned everything but can't seem to see what spring closes the throttle. I can push the governor arm forward and slow it down, but it pops right back open to about 1/2 throttle. Even with the engine shut off, the throttle remain a 1/2 open. Any ideas? The governor-link-spring is a mystery. I don't seem to understand it's function. How does it work?

Hi,
Try the 270962 manual at this link:
"K&T Parts House Lawn Mower Parts and Chain Saw & Trimmer Parts"
And go to the governor chapter to look for the correct control panel.
Peace,
Clarke

Thanks crigby,looks like a great info source. I'll see what I can figure out.