Watch the short video below to see how we overhaul a Stromberg 175 CD, then read all the details underneath.
As the proud owner of a classic Mercedes-Benz, you know that the performance and reliability of these legendary German cars depend on one crucial component: the Stromberg 175 CD carburettor. But did you know there are no fewer than 16 different variants of the Stromberg 175 CD, specifically for Mercedes models?
The Stromberg 175 CD, a Mercedes classic
The Stromberg 175 CD is not just any carburettor. It is a piece of German engineering that set the standard for classic Mercedes engines for decades.
The 175 CD variant was mainly used in Mercedes models from the 1970s and 1980s, including the 280SE, 280SEL, 300SE, 300SEL, 280SL, 280E and 280 Coupé.
The Stromberg 175 CD works on the constant-depression (CD) principle, also known as constant choke. Engine vacuum automatically regulates how much petrol is supplied, whatever the revs. That makes for exceptional reliability.
The 16 Mercedes variants, do you know your type?
One Stromberg 175 CD is NOT the same as another. Mercedes produced no fewer than 16 different versions, each matched to a specific engine type and vehicle application. Without the right specification you are literally fitting a carburettor that does not belong on your Mercedes, and the result is poor throttle response, a rough idle and wasted fuel.
The three best-known cap variants
In our workshop we see the same three cap variants time and again. The colour of the cap, a simple but crucial marking, determines much of the tuning characteristics.
Red cap (most common)
The red cap is the most common variant and is used on most standard Mercedes six-cylinder engines. This version is set up for moderate fuel delivery and is found on the 280SE and 280SE/3.5, the 280SL roadsters and standard 280E models. Characteristic: moderate jet sizes and a moderate float chamber volume, suited to everyday driving.
Blue cap (sportier set-up)
The blue cap turns up in the more performance-minded Mercedes models. This variant has slightly larger jets and is set up for higher revs and more fuel delivery. You will find it in the 280SE/3.5 with a sportier state of tune and in certain 280SL variants. Characteristic: slightly larger jets, optimised for more power.
Green cap (emissions-optimised)
The green cap was designed for models that had to meet strict emissions standards. It appeared towards the end of the Stromberg era and is set up for cleaner combustion. Characteristic: finer tuning, optimised for lower emissions, with a more complex calibration.
Common problems with the Stromberg 175 CD
After decades of service, these carburettors can show a range of symptoms:
- Hard starting, especially in winter
- Rough idle (fluctuating revs)
- Poor throttle response, sluggish acceleration
- Fuel leaking from the float chamber
- A worn or sticking poppet (fuel valve)
- Damaged or worn seals
The problem: many workshops fail to spot that your specific Stromberg variant needs a different approach from the others, and the result is wrong settings and frustration.
Our complete overhaul procedure
For every Stromberg 175 CD variant we follow the same meticulous overhaul procedure.
Step 1: identification and inspection
First we establish exactly which of the 16 variants you own, based on the cap colour, jet sizes and original Mercedes specifications. We document the current condition thoroughly.
Step 2: complete disassembly
The carburettor is taken apart completely. Every part is checked for wear, corrosion, damage and worn seals.
Step 3: ultrasonic cleaning
All metal parts undergo intensive ultrasonic cleaning in our Emag404 cleaning bath, made specifically for carburettor parts. This removes burnt residue, limescale, rust and dirt from every channel and drilling.
Step 4: replacing worn parts
Depending on your specific variant we replace the jets (exactly the right type), the float and float needles, all rubbers, O-rings and diaphragms, the poppet and poppet spring, the vacuum diaphragm (where needed) and the choke sealing rubbers.
Step 5: precision assembly and setting up
We reassemble everything with precision, paying special attention to the correct float level (critical for fuel delivery), the right idle setting and vacuum-testing the diaphragm.
Step 6: testing and final check
After the overhaul we test the carburettor extensively, with a visual check for leaks and a check of the float mechanism.
Why this make is so special
The Stromberg 175 CD really marks the end of an era. This is a carburettor from before electronic injection: purely mechanical, pure and simple, no computers. For Mercedes owners that is exactly the charm: no dependence on sensors or electronics, maintainable and repairable by craftsmen, with the characterful performance that lets you feel the engine at work. What's more, a correctly set up Stromberg 175 CD often performs better than many later electronic systems.
Contact and quote
Your Stromberg 175 CD deserves the best care. We know this carburettor inside out and have already overhauled more than 100 different Mercedes carburettors. You will find us at Huizerweg 49, 1401 GH Bussum, the Netherlands. Fill in the contact form for a free quote and we will give your Stromberg the care it deserves.