On 4 Aug, 20:01, Theo Markettos
wrote:
1-2 sheets - cuts out after 1-3s
3-4 - runs, some degree of misfire
5 - misfiring 60%+ of the time, but enough to run without load just about

Not familiar with this particular engine, but in general the magneto
gap affects the spark amplitude, but not timing. Again, in general,
the amplitude is not very important. As the other posters say the
carb is a good place to go, or indeed a new plug. To alter timing you
would need to move the coil radially around the flywheel.

In the old days it was common to put a "keeper" on the magnet when
removing the flywheel, but I think it is an urban myth - the magnetic
circuit is only closed when the magnet passes the coil.