Yes, it is normal. When you turn off the key, the solenoid on the bottom of the carburetor bowl prevents fuel from going through the main jet and into the venturi. During the last few revolutions of the engine, before it comes to a complete stop, the tiny bit of fuel still in the emulsion tube get drawn out. So basically there is nothing to prime the engine for the next start. Therefore it must be choked again. The reason for the solenoid preventing any fuel flow is due to the hot muffler being so close to the cylinders. When there is too much fuel, this is where you get after bang. After bang is when you get anywhere from a puff to a shotgun blast out the muffler. Some refer to this solenoid as an anti-backfire solenoid.
