As a follow up, I won't need to fiddle with the carburetor. The throttle stop screw I adjusted has a spring wrapped around it. The spring makes it hard for the screw to loosen when tightened, so I accidentally opened up the throttle and thought that I couldn't back out the screw any further.

The idle, which is in the 650-750 rpm range, surges to 1k rpm every 1-2 seconds, so I'm trying to figure that out now...