[Christ]

A few questions:

Did you gap the plug properly according to the specifications for your mower?

Are you aware of what gap the other plug had?

Are you aware of the materials used in the electrode of either plug?



The reason that I ask these questions is that the motors used for lawn mowers are governor controlled, but don't have variable ignition timing. Therefore, a colder or hotter spark would directly effect power and fuel economy. Colder or Hotter spark isn't necessarily determined solely by construction, it can also be affected by gap size, electrode density, and wear.