I have a 1982 Mercedes W123 (engine M102 - gasoline, 2.0L, 80kW, with Stromberg 175CDT carburetor). The car has been modified to run on LPG, the modification consists of adding a LPG tank, vaporizer and connecting the output of the vaporizer to the air intake of the engine (between the air filter and carburetor). Electric valves make sure that only one type of fuel is turned on (typical cold start procedure: switch to gasoline, start the engine, drive until the engine is at least 40C, turn gasoline off, drive until the carburetor is empty, switch to LPG).

The modification was done a long time ago and car worked perfectly. The problem started after I rear-ended another car, so it could be something bending or breaking (or it could be a coincidence).

The problem:

  • When cold, the engine idles rough, when hot (60C or hotter), it idles OK.

  • The RPM is limited to about 3200 - when the car is stationary (and in neutral gear), flooring the gas pedal only does to 3200RPM, but releasing it half way keeps the RPM.

  • The engine has little power. It takes forever to accelerate to faster than 80km/h and the car is especially slow when going up a hill. This is the same no matter which fuel (gasoline or LPG) is used.

What I have tried:

  • Adjusted the throttle linkage so flooring the pedal opens the throttle all the way.
  • Replaced spark plugs, spark plug wires, distributor cap and rotor arm.
  • Added oil to the carburetor (it takes oil designed for automatic transmissions).

Any ideas what could be wrong? Can this be because of worn out clutch?

1 Answer 1


This almost sounds like you have an obstruction somewhere in the intake path as it sounds to me that the carb either doesn't open all the way or it can't get enough air in even if the carb is fully opened.

CD175s have a (rubber) diaphragm - these get old, crack and tear after a while. That would be the first check I'd make.

  • While I did not risk taking the carb apart, I finally found a competent mechanic who managed to repair the engine. And yes, the diaphragm had two holes in it. Now the car is really quick (did not test top speed (yet), but acceleration is really fast).
    – Pentium100
    Jul 18, 2012 at 10:15

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