I wasn't running at full power at the time and my
understanding is that SAG is worse at WOT.

Bob W.

The electrical energy required to fire the plug is affected by cylinder pressure. The higher the cylinder pressure the higher the voltage required. The highest cylinder pressure for any condition will be at wide open throttle. Since that is the case, a slight reduction throttle will lower cylinder pressure and will restore normal ignition performance. Always a good test for poor secondary ignition performance.  

 

Lynn E. Hanover