R1 provides bias current for the zener, so it gives a stable voltage = 4.3V. There is probably not enough current
flowing out of the v.reg reference pin to properly bias the zener into its stable-voltage region without R1.
0v = 5v out
4v in = 9v out?
This makes no sense. You can't get 5V out for 0v in. To turn on the ckt properly, you need Vin at least 2V
higher than Vout. [D1 does nothing during normal operation, so don't confuse with that].
If OP reading something other than approx 9.3V [+/5%] out, then he has it wired wrong.