I need somebody to clear my understanding and confirm the operation of a Pierburg 2E3 choke system from cold engine to warm and back to cold.

I will attach a reference photo below.

There are 2 scenarios to debate on:

A - IDEAL case (aka "this I would like to happen")

Cold engine (-10 deg. C outside) -> The choke flap is closed and the fast idle screw (3) rests on the highest cam of stepper (2). We start the engine without touching the throttle pedal. Engine starts at fast idle (2300 rpm), thermo-time valve (TTV) kicks in heating the bi-metal coil at 12 V and then is shut off while bi-metal coil is now heated by coolant as the engine is warming up. The bi-metal coil forces the choke flap to open gradually and in the same time the stepper cam (2) rotates counter clockwise and screw (3) 'slides' to lower and lower cam thus lowering the rpm to 800.

So far we NEVER touched the throttle pedal and waited in neutral for the engine to warm up. Now we go for a short trip, park and stop the engine. Basically all happens in reverse, the bi-metal coil contracts closing the choke flap and forcing the stepper (2) to rotate clockwise and raise the screw (3) to highest cam, ready for a new cold start.

B - REAL case (aka 'semi-automatic')

Same as above with a couple of major differences: the spring that drives the stepper has no force to overcome the friction between the screw (3) and cams while the engine is warming up, respectively the bi-metal coil has no force to raise the screw to the highest cam while contracting after the engine is stopped.

We have to do 2 things:

1) drive after a cold start without waiting for the engine to fully warm up and so by using the throttle pedal, we raise the screw from cam each time allowing the stepper to rotate and the screw to rest next time on a lower cam;

2) before a cold start, we press the throttle pedal 1-2 times fully to allow the stepper to rotate and position the screw on a higher cam.

So what do you think ? What is true and what is not ?

I don't know how well the Jikov does this, but anything I've ever driven with an auto choke working correctly I'd have done/expected:-

1) Start engine and let it fire to run on full "fast idle".

2) Put on seat belt. Blip throttle to obtain a "required enrichment" idle.

3) Drive normally, and the auto choke reduces enrichment as the engine warms up.

i have the carb model and guess what Case A used to happen with me cold start the engine it would goo high but only to 1500 or 1200 rpm but it wouldn't go down even if i waited forever so i just waited for some time till i feel the engine is warm enough then i push the throttle pedal just one quickly and the rpm drops down to 800 and steady but after i cleaned my carb one i can't it back to that so i have so press the throttle pedal 3-4 times b4 i start it cold start of course then i start it and i have to raise the rpm myself using the throttle pedal until the engine is warm enough if i released the throttle pedal b4 engine is warm enough it just stalls...

you have a clear case of choke system not functioning properly.

there are many causes involved, some mechanical, some vacuum related, some electrical and some cooling related, because as you might know, the choke system for Pierburg 2E3 is a combination of springs and levers, vacuum tubes, electrical and coolant heated bi-metal coil...

anyways, after a lot of reading from Haynes carburettor manual, Pierburg 2E3 original manual and some russian sites showing in depth overhaul, I came to a DEFINITIVE conclusion that scenario B is the true one.

that is why I will post a PDF covering the entire process of repairing a 2E3 carburettor and a troubleshooting table for each and every defect.

Edited 26 September, 201114 yr by masster