The “Start” event node you are using, is only called once when the graph is enabled (on its start). To achieve what you want, you need an event that calling its output continuously (per-frame). As such that event would be the “On Update” event node. If you replace your “Start” event with the “On Update” event, your flowscript should work as expected.
On the other hand, to achieve what you want, it might be easier to create a Custom Event instead, like so:
You can then fire that event from your code like so: