Broken spark plug = poor idle

Maybe somebody else will benefit from this. My idle was intermittently poor, couldn't figure out what it was. Pulled a plug for a jetting check and was about to put it back in and just caught some movement in the electrode insulator out of the corner of my eye when I turned it back upside down. Sure enough the insulator was cracked all the way around about 4mm down and could move up and down on the electrode. Ran fine except at idle where it was probably partially grounding out up inside. At full throttle I assume the insulator was pushed back into position.

Yet another thing to watch out for but at least easy to check:face-icon-small-hap