My -nominally- 6/1 is a complete bitza.
It came with a bottom end that, according to the spec plate started life as a 3/1 hopper cooled version and the bigger top end.
With an iron piston it leaped about spectacularly, whether the flywheels for the smaller engine have smaller built in counter weights I don't know but changing to an aluminium one made a vast difference, no balancing required to run at 620 rpm.
Hopefully a 6/1's flywheels won't be over weighted with the lighter piston.
Does anyone know if the various models had vastly different counter weights?
Cheers
Stef