Its peeing down out there at the moment, so Im not off to take pics of choke 'in situ', just yet.....!
However, heres a few pics that may help anybody in future when dealing with these choke units....
1) overview of choke unit, removed:
2) view of inside, before dismantling:
3) showing the 12v heating element (was broken on this one - hence the rebuild):
4) shows outer wiring loom of choke heating element:
5) shows the internal parts of the choke element:
6) shows the finished article
The 'theory bit' :
When your engine is cold, the choke is ON (ie: the choke 'flap' is in the closed position) restricting the air intake into the carburetter throat and therefore making your fuel/air mixture richer. The choke is ON because, inside the choke unit is a bi-metal strip (imagine two rulers, on on top on t'other - one made from metal that expands and contracts quicker than the other, when heated/cooled. These are fixed together and curled up like a spring, similar to that inside a clock). The trailing end of this 'spring' is fixed to the operating lever of the choke flap and the
inside end is fixed to a rotable spline that is fixed by a grub screw accessible from the outside of the unit. This allows adjustment of unit.
Also inside the unit, under the spring part, is a tiny, delicate 12v heating element/coil. This is what is connected to the wire that goes to the choke housing and disappears inside it. This element is 'clamped' between two star shaped ceramic type holders and a flexy spring washer.
So..... engine is cold and choke is already ON. Start engine and 12v is passed through the little heating element, which heats the bi-metal spring and straight away starts to slowly expand it, thereby operating the choke flap and OPENING it, turning choke OFF. This happens slowly, during engine heat up phase.
Now, obviously, as engine heats up, your coolant gets hotter. This is where the little inlet and outlet metal pipes come into play (see thread starters original query). The warm/hot coolant is pumped through the choke housing (never comes into contact with the inside as its contained in a little water 'jacket') and keeps the bimetal strip expanded and therefore the choke is kept OFF during driving.
So the 12v element starts the choke turning OFF process and then the hot coolant keeps it off.
It is not unusual for the tiny element to break inside and therefore your choke will stay on longer than necessary, until engine fully up to temperature. This can cause excessive fuel use, amongst other problems.
Finally, when removing the choke unit, mark its position first. There are 3 x retaining screws fitted into 'slots' to allow adjustment (effectively you are preloading the bimetal strip when you turn the choke unit, allowing it to come ON/OFF sooner/later). Refit it to original position and test, before starting to fiddle with any adjustments.
Its quite easy to clean/check/overhaul these chokes, but they need to be adjusted carefully, to avoid a) choke not coming ON fully as engine cools right down or b) choke failing to turn OFF fully when heated up.
Ok, lesson over.... hope this helps someone?
WIKI please?
