Speedmaster spark plug holes improvement??

This will explain it:

Experiments showed that cyclic dispersion in spark ignition engines is inevitable because the turbulence of charge within the cylinder varies from cycle to cycle, the fuel-air mixture is not homogeneous and the exhaust gas residuals is not fully mixed with the unburnt charge. In particular, the formation of the first highly active constituents and the early flame development have a profound effect on the subsequent combustion. The formation of the flame kernel depends on the local fuel-air ratio, the mixture motion, and the exhaust gas residuals in spark plug gap at the time of ignition, which are not stable, but randomly fluctuated. This causes variations in duration of delay period of combustion and affects the early stage of flame propagation

In the early stage of flame growth, the flame is small and very sensitive to mixture conditions. If the flame nucleus is moved into the thermal-boundary layer surrounding the combustion chamber, then it will burn slowly. In addition, at a given flame radius, the greater contact with the wall will reduce the flame front area. Conversely, if the flame is moved away from the combustion chamber surfaces, it will burn more quickly. Therefore, it can be concluded that cyclic dispersion is increased by anything that tends to slow-up the combustion process, for example, lean mixture operation, inhomogeneous mixture, exhaust gas residuals, and low load operation.

In other words get that spark plug out into the chamber where it belongs!