Checking and adjusting the Pierburg 1B3 carburetor (Audi 100 C3)

Checking the fuel level in the float chamber

The position of the float in the float chamber is not adjustable. If a malfunction is detected, check the tightness of the float and the technical condition of the needle valve, replace the faulty parts.

Adjusting the idle speed of a cold engine

Warm up the engine.

Connect the tachometer.

Stop the engine.

Open the throttle valve fully by moving the profiled throttle control lever to the appropriate position.

Start the engine without pressing the accelerator pedal.

Check the engine crankshaft speed, which should be between 3600-1200 rpm.

Adjust the crankshaft speed if necessary using the throttle stop screw resting on the profiled throttle control lever.

Adjusting the starting clearances of the air damper

Remove the starter cover.

Open the throttle valve fully by placing the throttle control lever on the appropriate profile.

Connect a vacuum gauge and a vacuum pump to the air damper pneumatic drive and create a vacuum of 100 mbar in the pneumatic drive.

If the air damper pneumatic drive is hermetically sealed, the vacuum should not decrease by more than 5 mbar per minute and should decrease to less than 40 mbar.

Bring the vacuum in the air damper pneumatic drive to 200-300 mbar.

Using a set of feeler gauges, measure the starting gap of the first stage of the air damper, which for cars with a five-speed manual transmission should be 2.3±0.15 mm, for cars with an automatic transmission - 2.1±0.15 mm.



If necessary, adjust the correct clearance using the pneumatic actuator diaphragm stroke adjustment screw located on its cover (see photo).

Close the atmospheric hole of the air damper pneumatic drive with a plug, create a vacuum of 200 mbar in the pneumatic drive, which, if the pneumatic drive is sealed, should remain unchanged for at least 1 min.

Using a set of feeler gauges, measure the starting gap of the second stage of the air damper, which should be within 3.0 ±0.15 mm.

If necessary, adjust the clearance using the adjusting screw on the end of the air damper actuator rod.

Adjusting the throttle opening

The throttle position is adjusted at the factory, but if the adjustment is out of adjustment, it can be restored as follows:

• remove the throttle limit screw plug;
• connect a vacuum gauge in parallel to the vacuum regulator of the ignition timing sensor-distributor;
• start and warm up the engine;
• move the throttle control sector away from the idle stop;
• turn the throttle valve limit screw so that the vacuum begins to increase;
• turn the throttle valve limit screw until a minimum vacuum is obtained, then turn it back another half turn;
• adjust the idle speed of a warm engine as follows;
• install a new plug onto the throttle stop screw.

Adjusting the accelerator pump

Remove the carburetor.

Fill the carburetor float chamber with fuel and place a measuring cup with a funnel under the carburetor.

Move the throttle control sector away from the idle stop.

Slowly move the throttle valve from stop to stop ten times, spending approximately 3 seconds each time, thereby activating the accelerator pump.



Measure the amount of fuel in the measuring cup: in one cycle the accelerator pump should deliver 0.9±0.15 cm² of fuel.

Adjust the accelerator pump output if necessary by moving the accelerator pump drive lever cam on the bracket, after loosening the lock screw.

Adjusting the idle speed of a warm engine

Adjustment of the engine idle speed must be performed on a warmed-up engine with adjusted clearances in the valve drive mechanism, with the ignition timing set correctly.

Connect the tachometer and gas analyzer in accordance with the operating instructions.

Using the mixture quantity adjusting screw, set the crankshaft speed within 750±50 rpm.

Using the mixture quality (composition) adjusting screw, achieve a carbon monoxide (CO) content in the exhaust gases of no more than 1.0±0.5%. Restore the crankshaft speed to 750±50 rpm. If necessary, restore the specified CO content.