Here's one suggestion from the Internet. If you can find a place that has a reputation for fixing the detonation issues I'd send you head in. All in, all done including shipping shouldn't be over $200 bucks which is a lot less than a rod and piston and whatever else. Your call, but I wouldn't start it without at least a head mod and some big fat jets. If the timing is adjustable you may want to start off at full retard.
It sucks to get old
If you look close you can see Glamy at the dunes!
You might also want to fire a compression release through the head while it's apart. They're pretty cheap and I think it's as easy as making hole in the head and threading it in.
85 Tri-Zinger 60
85 ATC250SX
86 ATC250SX
87 ATC250SX
02 XR650L conversion
84 ATC 480R
Not your motor but check out this comp release, could it be be this easy? https://twistingthewick.wordpress.co...ase-by-wimmer/
Found it earlier thought i’d share
Shep
Awesome man! Last year I built a 84 atc480r. The big bore 2 strokes are something else!
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85 Tri-Zinger 60
85 ATC250SX
86 ATC250SX
87 ATC250SX
02 XR650L conversion
84 ATC 480R
I had a '80 YZ465 for a handful of years up until recently when I sold it. 2 words... Straight Nasty!