My Mum bought me an 82 KX125 brand new still in crate. (I was 17 yrs old) ...Had been riding an 81 YZ125 until then and the KX decimated the YZ in every department.
I kept the YZ for another year as a back up bike ........but never rode the hoppity Yam again.
83 kx125 broke clutch baskets......though I never had anything fail on my 82 .
Was living in South Africa then and a Kawa team mechanic remachined cylinder head squish shape.
The top of cylinder was machined/grooved to use YZ125 " O" rings in place of the head gasket.
Bike ran on methanol and with head mods had masses more drive out corners...a great bike....I really enjoyed it.
FYI..the 83 head gasket is thinner than 82 and could be interchanged for a tad more compression if desired.
Only time it shat itself was when I took it to the track so a prospective buyer could test ride it.
Rear shock was freshly rebuilt and had been quickly installed before heading to meet buyer.
During his test ride the bottom shock retaining bolt fell out and the shock went straight down into the ground and bent itself 45 degrees under the swingarm....
He bought the bike anyway...with a corresponding reduction in price..