It is usual to have just enough rotating inertia to prevent kickback during starting. How much that is, depends on the application. So, on mowers Victa uses aluminium flywheels and relies on the inertia of the blade plate. Briggs does the same. In special applications there may not be a blade plate: Victa adds a steel band around the flywheel of engines fitted to edgers, for example. The one that at first glance seems a bit odd is Honda: they use massive cast iron flywheels together with either a heavy bar blade or a similarly heavy blade disk, then use a decompressor as well. The reason for all those precautions against kickback is that they use a static ignition timing of 26 degrees BTDC, with an 8 to one compression ratio, which would kick very severely if not for the rotating mass and the decompressor.
The answer is that there are several ways of dealing with the issue - the important thing is not to take an engine specified for one purpose and fit it to a machine that operates differently.
