Neutral light will probably be the sensor in the back of the engine. Carefully remove wire (it'll probably break), unscrew, soak in WD40, wiggle a few times, refit, solder wires as necessary. Easy and quite satisfying.
Back firing, everything Frank mentions, and check all rubbers for splits etc.
A little TLC and she'll be hunky-dory.
Cheers,
Ali
Edit: Neil at Sigma can definitely do carb setup, etc.
[Edited on 19-2-2006 by ali]