Originally Posted by bluebye
The piston crown shows detonation, is the air filter intact and sealing well? Filter, box, and boots. Very important. Doesn't look like timing (advanced) to me, as the points wear and retard the timing.
this is cdi bike, it appears to has some detonation on the front of the piston - could be air leak or ignition too far advanced. both symptoms show similar damage.. usually airleaks cause damage more near the center of piston, and ignition problems on front side of piston (pics show damage to front side and it also looks like there's a good divot in the center of the piston). but you're right it's most likely an airleak on the dry side seal or cracked intake boot.. it definitely got lean more than once.
it's easy enough to take a quick look at the mag plate and see if it's been messed with - if it has, definitely do a timing check.