All these problems are so familiar lol. Regarding the starter, it could be a dead spot on the commutator (where the brushes contact the shaft within the motor). Mine used to click and then do nothing, but when it was out the car would spin up fine. I beleive this is due to the fact that when its out the car, the motor just spins on past the dead spot and carries on fine. When attached to the gearbox the flywheel increases the inertia and wont spin past the dead spot. Also, once stuck on that part of the commutator I had to get a screwdriver and turn the motor round a bit!! You can prolong the life by cleaning the commutator with a bit of fine wet and dry paper, but ultimately it is best to replace it.
As people have said already, the top sensor on the head indicated earlier is the temperature sensor.
The pipe exiting to air I would say was a previous owners bodge to try to fix the problems caused by all that muck coming out the breather from clogging up the carb. My jets were allways blocking up till I re-routed the breather into the catch tank!! I would personally do the catch tank trick, but I do beleive that the breather is meant to exit to low pressure air within the airbox. But mine has been fine exiting to atmospheric for 3 years now so I think its probably safe.
I wouldnt put a pipe down to the ground though. Unless you put a small air fliter on the end as any dirt kicked up may get into the engine as air pulses in and out from the breather.
All the best with the work anyways!
Si
