Sounds like it will need a rebuild if the piston is scored. Does not necessarily need straight fuel to score the piston, it it has been running lean or getting hot it can cause that as well.
A reminder why it's bad to turn off the fuel tap to stop the motor or to let it stall from running out of fuel.
Hello All
MF, I can't see that being the cause of that bad scoring. The only way I see turning off the fuel tap bad is when people do it with the throttle down at run and shut it down like that. From a moderate idle, I just can't see it provided the seals are ok and it doesn't revs its head off for long at the end.
with regard to oil, bynorm oil until recently was JASO FB oil. JASO FC is required to run 50:1 and even then I wouldn't recommend it. If you run a quality 2 stroke oil like Penrite MC2ST or KO2ST, or Castrol Power1 (I am using a bottle of TTS at the moment) you will never see any smoke while running at 25:1 (bit at start up somethimes).
It is important to note that FB and FC have same lubricity requirment, but FC has better detergency (less carbon).
Without doing a full blown failure analysis teardown my bet, aside from flat out cooking it due to marginal lubricity, would be the FB oil has carboned up the rings as well, one or both got stuck and then the massive heat from blowby took care of what little lube was left.
