Engine give weird "puff" when turning off ignition

I think the little pencil sharpener is actually a tiny sandblaster. you can recover plugs with a sand or bead blaster, but like loud said, they are never quite like new. Also MAKE DAMNED SURE you blow/clean all those tiny bits of sand/glass out of the plug before it gets anywhere near a bike.

I have one of them at work. I've had it for over 20 years. It works great! Yea, clean well before installing.