Choke

[c.k.]

does anybody know anything about automatic chokes. I have a 1992 mazda 323 and sometimes when i start it, the engine reves up to 2500or so. I believe this is the choke. After driving for a few miles or reving it up hard, it knockes off.

The car only has 38,000 miles on it (seriously) and is otherwise sound. Any ideas as to to where the choke it, or what it lookes like? OR any other information.

Thanks

 

[MANDATE]

If you recall manual chokes, you pulled a wire which in turn pulled on a lever/cam on the carburetter, this turned the spindle fitted with butterfly flap valve, partially closing this valve choked the air supply resulting in a richer mixture to enable the engine to start. As the engine warmed up it was up to you to release the choke bit at a time.
A automatic choke does the same basic function, on a cold engine the valve is already in the choked position, Heat from the circulating water is used in some form of thermocouple to make the linkage move to open the valve which should be fully open when the engine has reached operating temperture.
So have a look at the carburetter while someone presses the accelerator pedal, where you see movement of the accelerator cable thats where you will find the choke linking rod between carburetter and choke housing.
The choke housing will probably be aluminium, not more than 3 ins. in any direction ( I would think) and will have two pipes for the flow and return of water, although it could be mounted some other way where you cannot see the pipes. Probabley have circular cover on one side.
You could buy kits to change from automatic to manual at one time.
Having said that, it sounds as though yours is working in principle but needs tweaking

 

[AdamW]

What about with fuel injected cars? There you have no carburettor, where is the choke in this case?

 

[noflame]

With modern cars there is no choke at all in the old sense. Now you have an array of sensors which know what conditions the engine is operating under and feed this back to the ECU.
On a cold start the engine/coolant sensor will tell the ECU the engine is stone cold, and the ECU will then richen up the mixture accordingly.
As operating temp rises the ECU then leans the mixture off accordingly and much more efficiently than an old style choke could ever do.
If you have a modern injection system cold star problems can usually be traced back to temp sensor failure-the ECU thinks the engine is warm and sets the fuelling parameters accordingly.Modern intake systems are also a lot more sensetive to air-leaks than old ones as well which can upset fuel/air ratios.