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Problem

Holed piston.

Actual/common cause

Timing too far advanced/weak jetting/air-leak/too much two-stroke oil.

Solution

Clean the crankcase out as best you can, removing the mag housing to do so if possible.

Block the hole by inserting a Roofing Bolt (M5, M6 and M8 are the sizes I carry) and securing with a nut and large washer behind. You'll need plenty Loctite and some gasket paste would be beneficial too.

Complications

On assembly try to use two gaskets for the head and/or base to accommodate the head of the Roofing bolt and lower compression.

Unless you've found and fixed an air-leak, retard your timing a few degrees and either fit a bigger main jet or run with the choke on to get you home.