I thought the BX was an electric buggy. You sure it is not a Nitro Evader ST?
http://manuals.hobbico.com/dtx/dtxc0062-manual.pdf
The one with the spring on it should be the Idle Set Screw. The one you refer to as the main one, is you HSN(high Needle). The one that is left on the rotary part of the carb is you LSN. First step is to get it to start. I don't know the factory settings for that carb. If it starts the just make sure it is spitting fuel out the stinger and go from there. I like to start with the HSN and monitor my temps. I don't like to tune by temp but it will get you to a safe zone. Once you have the HSN close then move to the LSN. If you pinch the fuel line were it enters the carb and it revs up and dies immediately then the LSN is lean. I like for it to run 4-5 seconds after pinching fuel line.
I would also put a fresh glow plug in it.
Hope this helps.
T.