If you are an old hot rodder / off road biker , you have been thru this exercize.
Not all plugs are created equal -not even same brands - When I ran Hodakas - the first thing to go was always the plug - simply ruined from heat and contaminants.
You could pull it - clean it, look till you turned blue and see nothing wrong --but it ran ****ty.
change the plug - presto -- back to full power .
If you are just tinkering and it all runs starts etc., nicely --leave it alone .
If you are on a quest for max power - try different plugs/gaps etc..
for all around use - I set all my ZDZ's at .025 -on Brisk or NGK.
I make damn sure I don't overheat or over prop (overheat ) and use (now ) 32-1 syn right from the get go - so far the best looking pistons as far as being clean on tops / sides - no burned look in header or mufflers .
The plugs also look new except for being darker on the porcelain