Don't have anything else connected to 324's in- pin, just have the LED and the feedback resistor (start off with megohms)
Because the photocurrent comes out the LED in reverse to the current that lights it, you need to point the diode 'upwards', with the blunt end to deck (where +pin is connected).
How it worx: As the LED sends photocurrent into the ground, it creates a corresponding 'vacuum' at the LED cathode (connected to the in- pin, monitoring the uV). An equal current is by now flowing through the feedback resistor, tipped upwards now, because the - pin is being sucked down a few uV by the vacuum. The current coming out the resistor into the LED fills the 'vacuum', just enough for the - and + pins to equalise.
The resultant 324 output voltage is proportional to illumination and is very very linear. (as opposed to a PV detector in 'open circuit voltage' mode which is very non-linear)
You can use the input threshold voltage of the C51 as a crude 'comparator'.