Bodgernomics

it's to warm the inlet manifold.

Is the water not there to warm up the inlet manifold/carb so that the auto choke switches off once the engine is warmed up? - would also explain the fast idle.

Well I superglued the plastic thing (which contains a metal thing) together and so far so good...

Now it's just a matter of getting the stud out of that water pump (still held together with one bolt and two zip ties), although I reckon it'll get me to work tomorrow 12 miles away when I can get a fessional onto it.

I'll track down that plastic bit (with metal bit inside) too as having something like that superglued does not fill me with confidence :s

No it warms the manifold to keep the petrol from pudling, condensing on the cool wals, so it is burned by the engine. It should make more power now, run a touch weak at lower rpm and have higher hydrocarbons at idle.

That's the wonders of the spark ignition internal combustion engine. A cold engine runs better if you heat the inlet manifold, and for ultimate eficiency on a hot engine you need a cool dense charge of air.

Hmm, I have a water jacketed inlet manifold and no choke at all, much less an auto one (old V8). I've always assumed this was to warm the air to a constant temperature and avoid icing due to pressure changes.

What's the actual reason, anyone know?

Ah, that's what it's for!

Yes to keep liquid fuel vaporised.... It improves "running", emissions, economy. But costs power.

well it idled like s*it without it on there, but there was something more to the device - some spring loaded gubbins!