This Spark Plug Gap Coin gauge tool is one of the easier options for gently increasing the spark plug gap of any j-gap electrode.
 
The sliding gap scale provides just one tool vs. multiple feeler gauges to measure and adjust from 0.020 to 0.100 gap.
 
The recommended gap for a high-performing 2-stroke outboard is between 0.030" and 0.042". However, manufacturers' recommendations for specific engines can vary. 

A good starting point is 0.035". You can experiment with different gaps to see what works best for your engine. 

The larger the gap, the more voltage is needed to bridge the gap. If the gap is too wide, the arc won't strike, causing misfires.

Note: When gapping a plug be careful not to damage the precious metals tip, like iridium, platinum, silver, or ruthenium. Or weaken the j-gap by repeatedly bending open and closed while finding your ideal gap.
 
Contact Mike Hill at STVracer@yahoo.com