Engine running away after carb rebuild....

Good result.
To help people's understanding, modern gas engines have a throttle plate which closes off tightly. The idle speed is controlled by the Idle Air Control (IAC) which is an electric motorized valve which leaks air around the throttle plate. You can speed up the engine by pulling a vacuum hose, say the big one to the brake booster. The IAC will go full-closed, but the engine will still idle too fast. But, the engine will run fine since the engine controller will just add the required fuel. If you run that way long (~30 sec), the computer will likely trip a code "unable to control idle speed". When my 1996 Plymouth 2.4L was idling way too fast, even w/ the IAC port plugged, I found the air leak by spraying water around until the speed changed. The intake manifold gasket had become brittle and lost chunks, causing a large air leak.