Mercedes W123 engine “jumpy” when cold

Question

I have a weird problem with the engine of my W123 (the engine is gasoline, 2L, 80kW with a Stromberg 175CDT carb).

When the engine is cold (less than ~50C or so), it acts weird. When I want to accelerate from slow speeds (first, second gear) and press the accelerator, the car delays a second or two and then jumps forward. This happens once or twice and then does not happen until I turn the engine off and then start it again.

EDIT: As it is now much colder outside, I think I have found the actual problem symptom. When I start the engine, while it is cold, if I quickly press the accelerator (without the car being in gear), the engine just stops. After a minute or so of warming up it works properly.

Answer 1

Your automatic choke has failed and is not closing as it should when cold. If you want very much to keep the car original or just don't want to deal with a manual choke, then you'll need to find a replacement automatic choke actuator that works for the Stromberg. If, on the other hand, you'd just like to get the car functional again, then you can easily install a manual choke cable and learn to operate it effectively.

Answer 2

http://www.autozone.com/autozone/repairguides/Mercedes-Coupes-Sedans-Wagons-1974-1984-Repair-Guide/Carbureted-Fuel-System/Carburetors/_/P-0900c152800ae88c . Because of the age of the vehicle you will be unlikely to find someone to answer your question fully. I have not even seen a Stromberg carb for many years. The link above will bring up a good guide to enable you to check your carb out.

Answer 3

Most likely your carb needs some cleaning. These older style carbs has a few "holes" which could be stuck from like rust from tank.

Remove the carb and carefully clean it. I would also add/replace the fuel filter.

You could use etil alcohol for cleaning.