YZ 125 Engine Question?

[SMF]

I have a 2001 YZ125 and have a question on its rebuild of the motor. I
bought the bike from a  guy who told me I needed to mix race
gas(111oct) and pump gas in order for it to run like it was suppose to because of
its engine mods. Well I was running real hard racing on wide open
throttle and gradually lost power until it just quit. I tried to restart and
low and behold there was no compression.
   I removed the top end and pee yew does it smell burnt. My question
is how do you determine if the lower end needs to be rebuilt? The small
plastic parts screw into cranks counter balancer at the base of the rod
appear to have melted slightly causing the burnt smell. By the way I
did win the race, but when I asked my opponent if he noticed any blue
smoke he said no. Must have neglected to agitate mixed gas can before
dispensning into tank.
  OOPs
   
SMF

[rubenjohnson]

Can a yz 125 engine fit a yz 80 frame? Yes it can! How much work I do not know. I saw an 80 a few years back with a 125 engine in it.