Hi Adam,
M122X possibly 1989 to 1994
M120X → nominal class ≈ 120 cc
M122X → nominal class ≈ 122 cc
121–122 cc (often quoted as 121.5 cc)
As far as I know
Parts are functionally M120X
Every confirmed M122X owner who has rebuilt one has found that:
carburettor
crank seals
ignition
piston & bore
gaskets
…match M120X specifications.
In practice, suppliers, rebuilders, and forums treat M122X = M120X for parts purposes.
From what I've read the carbies are different or jetting and governor linkage.
A local mower shop should be able to clean the carby or do it yourself,
Old mowers are cheaper than parts ,usually you can find one for $10. or thrown out ones in scrap metal.
Cheers
Max.
