Rode hard & Put up wet

[67L36Driver]

And those four headless 5mm screws, to keep the case halves from rotating...makes it less of a fight.

I been using three. [emoji6]

 

[av8or3]

I don’t know, but I’m thinking preignition erosion causes those micro pits/pockets, and that is due to the octane loss in old stale fuel & a lean mixture.

The piston has a huge black “spot of death” under the crown, and carbon was caked up everywhere for making hot spots.

Wouldn’t take a couple of tanks of foul gas on a hot day to do that, plus with all the chain & clutch noise, you’re not going to hear it pinging like a car.

They’re just powered hand tools, run ‘em like you stole it!

I’m guessing wrong heat range spark plug. I personally have “holed” 2 pistons on a Yamaha RD350 by putting the wrong plugs in it. Even if the plugs are correct a broken or cracked insulator can cause the same thing. Look hard inside the nose of the plug and see if you can find little balls of aluminum.