I believe the center thing may be the clutch. More modern Yanmar
engines have two such cables, one is throttle and the other is the
clutch. The clutch is engaged/disengaged by pulling it out or pushing
in on a axle-like thing below the throttle. Perhaps this works the
same. Maybe it is a push pull thing instead of being a turning lever.
I vaguely remember something like that in the Yanmar service manual.