I had it off last night and there doesn't look to be any adjustment at all...open the throttle and the slotted section on the carb turns a small peice of plastic which slots into the TPS sensor which in turn, turns.
You can stick a flat head screwdriver in the sensor and turn it manually but it only moves as much as the carb would move it so I don't see how there can be any further adjustments made to it.
Anyway, whilst messing around with that I knocked a wire (very slightly) which revealed the full extent of the previous owners botch job on the wiring (see image below).
This is the wiring for the rear cylinder coil. No connection on it at all, it was loosely fitted into the female connector and secured with a bit of used electrical tape!
I'm going to tidy it up tonight. Could this explain why my headlight doesn't work and the rear light stays on? Or maybe not...