Hi,

You do not call bit_delay after you have found the start bit.  This
causes all 8 data bits to be sampled in rapid succession.

Proposed correction:
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start_bit   btfsc      ser_in,2
            goto       start_bit   ;look for start bit
            call       start_delay ;get centre of start bit
            btfsc      ser_in,2    ;look if still low
            goto       start_bit   ;false input start again

==>         call       bit_delay   ;Wait until middle of first data bit

            movlw      8           ;load counter for 8 bits
            movwf      bit_cntr
            clrf       rcv_byte    ;clear recieve byte
recieve     btfss      ser_in,2    ;get bit
            bcf        c,0         ;clear carry if bit is zero
            btfsc      ser_in,2
            bsf        c,0         ;set carry if bit is high
            rrf        rcv_byte,1  ;rotate carry to high bit in recieve
byte

==>         call       bit_delay   ;Wait until middle of next data bit

            decfsz     bit_cntr,1  ;if counter not finished get next bit
            goto       recieve
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Hope this helps!
Niki