your circuit is very bad quality unstable one, when you more you hand over it, it may go out of FM range, really not easy 2tune, also 5km??? you can try for a distance of 500m. 5km is not an easy task, involves stable oscilators, filters, power amp and antenna..
Wow! Your junk box has a lot of precious things. I an searching this 3866 from 3 yrs ago. It is great for long range. It has 1 watt RF output capacity. And it transmit easily 2-3 km in normal FM receivers. SHARE YOUR JUNK BOX WITH ME DEAR! Search 3866's circuits in google.
actually it will have a gain of 3. IIRC, all that's required is for the device to have a gain greater than unity to oscillate, but it's generally understood it should be at least 2.