Crazy Idle

Not necessarily an air leak. I had a similar problem and went to extremes looking for the leak. What I found was wear, probably from many miles of vibration, in the slots where the pin and idle speed screw contacts the carburetor slide (barrel). It would allow the slide to twist slightly and when you backed off the throttle it would occasionally jamb on the screw tip and/or alignment pin holding the throttle open. I used a Dremel and 400 sandpaper, smoothed the rough edge and stopped the problem then later replaced the carb. Just my experience but be sure there's no air leaks too. They're the most common cause of a fast/erratic idle and with a newer engine I doubt you've run it long enough to experience wear in the carburetor. Also air leaks are not restricted to the intake area. Crankshaft seals can leak giving the same symptoms as a leak around the carb/intake. To check for this remove the magneto and clutch side cover and check for oil.
Tom