Transfer function and frequency of Common-drain Colpitts with ballast coil
When you have L2 (250 uH inductor) connecting source to ground, this is the dominant oscillation mode for this circuit. L2, C2 and C6 form a high impedance parallel tuned circuit that has a resonant frequency of 300.775 kHz. L2 (8 mH) is there to bias the gate at 0 V but still allow an AC voltage to appear on the gate via C1.

When you swap out the 250 uH for a 330 ohm resistor you are back to the standard common drain Colpitts oscillator and L1 (8 mH) does indeed become part of the resonant circuit.

It looks similar to this Hartley oscillator except the 8 mH inductor is replaced with a bias resistor: -

http://www.next.gr/uploads/77/OSHA972.jpg

There is also a protection diode in case of excessive gate currents.