Help with beaming

[Paul McKay]

Hi
Can someone show me where I'm going wrong with the following. The piece is
in 2/4. I would like the default beaming for some sections (where there are
lots of eighth notes) to group them in whole bars but in sections where
there are lots of faster notes, then a beam ought only to span a quarter
note. In this example, if I ask for the first bars to be beamed in whole
bars, an extra beam appears in the following bars which joins all the fast
notes together. I would like the latter bars to continue to appear as they
do in this example, but for the first ones to appear all joined up.

Thanks in advance
Paul McKay
%%%% example
\version "2.22.0"
\language "english"

firstTuplet = {
    \once \override TupletBracket.bracket-visibility = ##t
    \once \undo \omit TupletNumber
}
global = {
    \key fs \minor
    \numericTimeSignature
    \time 2/4 \partial 8
    \override TupletBracket.bracket-visibility = ##f
    \omit TupletNumber
}
leftB = \relative {
    \set Score.currentBarNumber = 65
    \set Timing.beamExceptions = #'()
    \set Timing.baseMoment = #(ly:make-moment 1/8)
    \set subdivideBeams = ##t
    % If you uncomment the next line, the beaming on the first 3 bars is
correct but
    % there is an extra beam in the middle of the next three bars
    %\set beatStructure = #'(4)
    r8
    |%{65%} g'8 e'e, e |%{66%} cs cs' r4 |%{67%} c,8 a' a, a
    \set Timing.beatStructure = 2,2
    |%{82%}  \repeat unfold 3 { r16 a32 b cs d e f \firstTuplet \tuplet 3/2
8 { g16 fs e fs e d } }
}
    \score {
        { \global \leftB }
        \layout { }
    }