The need to adjust the carburetor is indicated by unstable engine idling or no idling, increased fuel consumption and, as a result, an increase in the amount of CO in the exhaust gases, engine failures and poor acceleration of the car.
Idle speed adjustment is carried out on a working engine, with adjusted valves and a correctly set ignition timing. The engine should be warmed up to operating temperature, the choke is fully open, and the air filter is in place.
Preparatory work
The idle speed is adjusted simultaneously with the setting of the minimum level of CO in the exhaust gases, therefore, a gas analyzer is required for correct adjustment. You will also need a tachometer and a short slotted screwdriver.
If there are still factory plastic plugs on the carburetor adjusting screws, they must be removed. To do this, unscrew the screws completely, remove the plugs from them and tighten them all the way.
Adjustment
Unscrew the screws approximately 3 to 4 turns and proceed with the adjustment. First, use the mixture amount screw to set the engine speed at 750 - 850 rpm. When screwing in the screw, the revolutions will increase, when unscrewing, it will decrease.
Next, insert the probe of the gas analyzer into the exhaust pipe and, using the amount screw, achieve the readings of the device in the range from 1 to 1.5% of the CO content. When screwing in the screw, the CO content decreases, and when unscrewing it will increase.
Since when adjusting the mixture quality screw, the engine speed will decrease, then with the quantity screw, restore the speed to 900 rpm. and check the CO level again with a gas analyzer. If the CO level is higher than 1.5%, then again adjust the quality screw to the required value.
Adjustment work must be repeated until at idle engine speed 850 - 900 rpm, the CO level is not established within 1 - 1, 5%. It is impossible to lower the CO level below 0.4%, since gaps in the operation of the cylinders will begin and the CH level will increase.
If no gas analyzer is available, adjustments can only be made using a tachometer. Using the quantity screw, also set the engine speed to approximately 800 rpm, then tighten the quality screw until the engine starts to run unstable. After that, unscrew the quality screw back by about 1 turn, no more.
If the engine speed drops, turn the number screw back to the previous level and repeat the adjustment until the optimum results are achieved. With this adjustment, the CO level will be set at about 2%, which is in line with the norms.
After completing the adjustment work, check the operation of the engine, for this you need to sharply press the gas pedal all the way and also sharply release it. The engine speed should increase without the slightest dips and then, when the pedal is released, set at idle speed.
If the engine stalls or runs unstably, then use the number screw to slightly increase the idle speed, but not more than 950 - 1000 rpm. After that, the carburetor adjustment is considered complete.
