i dont think there ever was an acoustic version of earth wind and fires classic september,
but i love the song and i love playing acoustic covers of songs,
and this is what i worked out to be right...    
    (this may be a bit off key, but just change the vocals to fit)

(dont start playing until syllable 2 of remember)

          E (022100@1)      A (x02220@1)   G (320003@1)      EDo (022100@1)you remember the 21st night of september?
         A (x02220@1)          G (320003@1)         ELove (022100@1)was changing the minds of pretenders
      A (x02220@1)        B (x2444x@1)     F# (244322@1)
While chasing the clouds away

Bridge: F# G A

                EOur (022100@1)hearts were ringing
       A (x02220@1)          G (320003@1)         EIn (022100@1)the key that our souls were singing.
      A (x02220@1)           GAs (320003@1)we danced in the night,
   E (022100@1)           A (x02220@1)             B (x2444x@1)    F#Remember (244322@1)how the stars stole the night away

        F# (244322@1)name="chord_320003@1">G A (x02220@1)E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - say do you remember
E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - dancing in september
E (022100@1)        A (x02220@1)          B (x2444x@1)    F#Ba (244322@1)de ya - never was a cloudy day

        F# (244322@1)name="chord_320003@1">G A (x02220@1)                EMy (022100@1)thoughts are with you
        A (x02220@1)             G (320003@1)               EHolding (022100@1)hands with your heart to see you
      A (x02220@1)          GOnly (320003@1)blue talk and love,
   E (022100@1)          A (x02220@1)           B (x2444x@1)      F#Remember (244322@1)how we knew love was here to stay

        F# (244322@1)name="chord_320003@1">G A (x02220@1)      E (022100@1)              A (x02220@1)           G (320003@1)                 ENow (022100@1)december found the love that we shared in september.  
     A (x02220@1)           GOnly (320003@1)blue talk and love,
   E (022100@1)       A (x02220@1)          B (x2444x@1)     F#Remember (244322@1)the true love we share today

        F# (244322@1)name="chord_320003@1">G A (x02220@1)E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - say do you remember
E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - dancing in september
E (022100@1)        A (x02220@1)          B (x2444x@1)    F#Ba (244322@1)de ya - never was a cloudy day

E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - say do you remember
E (022100@1)        A (x02220@1)          GBa (320003@1)de ya - dancing in september
E (022100@1)        A (x02220@1)                B (x2444x@1)     F# (244322@1)             F# (244322@1)name="chord_320003@1">G A (x02220@1)E... (022100@1)Ba de ya - golden dreams were shiny days