Adjusting the Solex Zenith 2B4 carburetor (BMW 5 Series E12)

Adjusting the starting clearance of the air damper

Remove the starter cover.

Move the lever to the air damper pneumatic drive and check the air damper clearance with a 4.0-4.4 mm drill.

If there is any deviation from the norm, achieve the proper clearance using the pneumatic drive adjusting screw.

Auxiliary starting device

Checking the mixture quality corrector

Remove the mixture quality corrector and apply 12 V to the corrector for at least 2 minutes, short-circuiting the valve body to ground.

The corrector needle should extend.

Cool the corrector to a temperature of 2041 and check the protrusion of the corrector needle, which should be within 2±0.5 mm.

Checking the actuator needle protrusion

Remove the actuator (automatic adjustment valve) and check the protrusion of its needle, which at a temperature of 20°C should be within 4-6 mm

Checking the pneumatic drive of the throttle valve of the 1st chamber

Check the spring pre-tension: dimension "A" should be 23 mm. If it deviates from the norm, adjust the correct dimension with adjusting nut 1.

Check the gap "B" between the throttle control lever and the stop screw, which should be 4.5-5.5 mm. If necessary, set the specified gap by changing the length of the threaded rod 2.

Checking the fuel level in the float chamber

Remove the carburetor cover and gasket.

Measure the gap between the highest point of the floats of the 1st and 2nd chambers and the mating surface of the carburetor with a ruler, which should be 28 and 30 mm, respectively. It is adjusted by bending the tongue and levers of the float.

Adjusting the opening of the throttle valve of the 1st chamber at idle speed

Tighten the mixture quantity adjustment screw 1 (see photo) until it stops.



Using the stop screw of the throttle valve 3 of the 1st chamber, set the crankshaft speed to 550 rpm. Using the quality adjusting screw (composition of the mixture) 2, after removing the plug, achieve a CO content in the exhaust gases of 2.2%.

Use adjusting screw 1 to bring the crankshaft speed to 900 rpm.

Check if the CO content in the exhaust gases exceeds 1%.

After completing the adjustment, install a new plug into the hole for the mixture quality (composition) adjustment screw.

Adjusting engine idle speed

Using adjusting screw 1, set the engine crankshaft speed to 900 rpm.



Check the CO content in the exhaust gases.

If necessary, use the mixture quality (composition) adjustment screw 2, after removing the plug, to achieve the proper CO content in the exhaust gases.

Using screw 1, restore the crankshaft speed to 900 rpm and check the CO content in the exhaust gases again.

Repeat the above operations until the CO content in the exhaust gases is no more than 1% at a crankshaft speed of 900 rpm.

(The original article is located on: «BMWMan»)