Your capacitor is twice the capacity, so it's going to take twice as long to charge up enough for the Flashing LED to fire, which switches on the motor, for about half a second. A smaller capacitor will charge quicker, and only has to provide enough current to spin the motor, since the solar panel can't provide it directly. The 1 farad cap might still work, but suspect it would need hours in low light to charge up enough for the initial pulse to the motor. You could add another solar panel in parallel to increase the charge current...