If he actually "adjusted" the carb, that might be the problem. This carburetor is completely non-adjustable. Lets start by checking the idle screw on the side of the carburetor to see if it may have been loosened. The screw should be all the way in, as it's simply a fixed jet.
Was it flipped before or after the tune-up?
Let me know and we'll continue.
Idle speed, or idle mixture?
What is the float height set at?
There should be a metal tab on the float the needle hangs onto by a wire. The metal tab is the adjustment. The float should tilt slightly down with the hinge pin being the high side. Use an 11/64" drill bit as a gauge between the end of the float opposite the hinge pin and the body of the carburetor with the gasket removed.
This pic illustrates what I mean:
Also, is the idle screw at the side all the way in? It's pretty common for it to be loosened as an attempt to adjust, so I just want to be sure. That would interfere with the transition between idle and high speed.
How old is the fuel that you're running?
Should be .004" on both. If they're set a tad loose it wouldn't make noise, but it would slightly reduce the amount of time each valve is open.
Does this miss occur over level ground? Or rough? Or does it matter? Do you see any recurring circumstance in which it seems to happen?
That possible, but I would have thought the tech would have checked the governor. Is this using a centrifugal clutch or a torque converter? Do you know what rpms the engine is attaining? Most centrifugal clutches like Comet will engage around 1850-2200 rpms. If you damaged the spring in the flip, that could cause erratic engagement.
You can bend the tabs indicated by the arrow to adjust high and low speed. Left tab adjusts high speed, right adjusts low. Bending tabs to the left decreases, bending to right increases.