How to Adjust the Idle Trimmer

How to Adjust the Idle Trimmer

Gasoline engines can be equipped with a carburetor or fuel injection system. In the case of the carburetor, it is well known that during operation of this system, periodic adjustment of idle speed is necessary. As for the injector, such a power system is controlled by an ECU, that is, the need for additional configuration is eliminated.

However, in practice, the situation is somewhat different, since quite often there is a need to adjust the idle speed on the injector. Malfunctions are manifested in the form of unstable operation of the engine idling, the speed is floating, the engine may stall after starting, overspending fuel in case of over-speed of the twentieth, etc.

Next, we will talk about how to adjust the engine idle speed on an injection and carburetor engine, and also consider the features and nuances of setting idle speed on engines with the specified fuel supply systems.

How to adjust idle speed on a carburetor

Let’s start with a simpler dosing system. The main advantage of the carburetor is deservedly considered the ability to quickly service the device with their own hands, using the minimum set of improvised tools.

To adjust the idle speed in this case, you will need to have several keys and screwdrivers. The main task will be to set such revolutions when the engine is able to work stably, while the crankshaft speed will be the minimum possible for stable operation of the unit.

Let’s look at the adjustment of the Solex carburetor. First of all, it is desirable to have a tachometer that will help determine the frequency of rotation of the crankshaft. On some cars, such a device may be absent constructively, while on others it is included in the standard package and is located on the dashboard.

  • So, before starting manipulations with the carburetor, the engine must be warmed up to operating temperature.
  • Then you need to completely drown the "suction", the air damper must be in the fully open position.
  • Next, the engine shuts off, and then on machines without a tachometer, an external device should be connected in accordance with the instructions and recommendations.

In some cases, you can use a multimeter tester. The positive output is connected to the output K on the ignition coil, the negative is connected to ground.

  • Now the engine can be started, after which it is necessary to turn on the dimensions, main beam, set the maximum fan speed of the interior heater, electric heating of the windows, etc. In other words, it is necessary to use energy consumers. After that, you can proceed to the idle setting on the carburetor.

As a rule, for most systems of this type, the idle speed is 750 – 800 rpm. It turns out that it is necessary to set the idle speed within the specified limits, and the internal combustion engine should work stably.

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To do this, rotate the adjusting screw on Solex, which is responsible for the amount of fuel-air mixture. At the end, the crankshaft should rotate at a frequency of 750 – 800 rpm. However, in many cases, the adjustment does not end there.

On the specified screw there can be a separate plug made of plastic, which you need to remove. This can be done by piercing the plug with an awl, after which a metal hook is pushed into the hole for extraction. You can also screw a self-tapping screw into the plug, and then without any difficulty remove the element.

Before starting adjustments to the XX, the quality screw should also check the correctness of the ignition setting (ignition time, SPD), the condition of the spark plugs and the candlelight armored wires. You will also need to exclude the possibility of third-party air leakage. In parallel, you need to be prepared for the fact that the adjustment will need to be repeated several times until the desired result is obtained.

The whole process is as follows:

  1. At the very beginning, you should turn the quality screw with a flat screwdriver so that the crankshaft speed increases to a maximum. To do this, turn the screw gently clockwise or counterclockwise. The main thing is to find such a position of the screw, the maximum speed of the twentieth code. This can be determined by the tachometer or orientated by ear (in the absence of instruments for determining the speed of the crankshaft).
  1. Now you can start to turn the screw the amount of the mixture, ensuring that the speed was at around 900 rpm. Tightening the screw clockwise causes the throttle of the first carburetor chamber to open slightly, resulting in an increase in engine speed.

If you unscrew the screw counterclockwise, then the shutter is closed, the speed will decrease. It turns out that it is necessary to find the position of the adjusting screw for the amount of the mixture at which the revolutions are at around 900 rpm.

Video: How to Adjust the Idle Trimmer


  1. Having set the speed, we turn to the quality screw. The specified screw is twisted so as to obtain 750-800 rpm If you immediately failed to achieve the desired indicator, you should repeat the setup procedure from the very beginning.

We add that when installing an abnormal carburetor on the engine or in case of carburetor repair (cleaning, replacing screws, jets), before starting the adjustment, first fully tighten the quality screw clockwise, and then release it back 3 or 4 turns. Only after this can we proceed to further settings.

Additional recommendations for setting XX on the carburetor

After the tuning process has been completed, you should check the operation of the engine not only on the XX, but also taking into account other modes. This means that the set of revolutions with a sharp or smooth pressing the gas pedal should occur smoothly, without failures and failures. Also, the engine should not stall after releasing the accelerator pedal sharply.

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Any dips or pauses are a reason to repeat the settings. The first step is to return to adjusting the quality of the mixture, enriching the mixture with a quality screw. With this enrichment, you can increase the speed to around 900 rpm. It is worth noting that high-quality and accurate tuning allows you to reduce the overall toxicity of the exhaust gases of the carburetor ICE.

In some cases, a situation arises when it is not possible to adjust the idle speed with screws of the quality and quantity of the mixture (there is no obvious clear reaction of the engine to the rotation of the screws or these reactions are completely absent). This indicates a problem when fuel enters the carburetor chamber and the engine is running, but the mixture does not flow through the idle system.

Such a malfunction can occur when the carburetor solenoid valve is not fully screwed in. Also, the plug of said valve may not be securely installed. As a result, the fuel passes by the idle jet, which is installed in this valve or its plug. Another jet XX can be incorrectly selected, have a hole too large, etc.

To check this, you will need to disconnect the wire from the solenoid valve on a running motor. Normally, the engine should stall. If this does not happen and the motor continues to work, then the valve itself needs to be diagnosed. If there are no problems with the valve, then you will need to set the fuel level in the float chamber, and also check the needle valve. Then the carburetor setting should be repeated.

We also note that sometimes it still fails to achieve correct operation in all engine modes. In other words, after setting idle, problems begin in transient conditions, with sharp accelerations, etc. In this case, you may need to finalize or tuning the carburetor. Sometimes a problem can be solved only by replacing the dosing device with a more suitable or serviceable analogue.

Injection engine adjustment and idle

On engines with an fuel injection system, as a rule, malfunctions do not occur immediately and tend to progress gradually. Typically, the driver notices that the car begins to respond with a delay to the gas pedal, the revs idle, the gas mileage increases, the engine loses power, the power unit may not work smoothly in different modes, etc.

Various malfunctions can lead to such symptoms, so it is necessary to carry out computer diagnostics of the engine, check the ECM sensors, eliminate air leaks and general problems of mixture formation (poor and rich mixture), nozzle contamination and other reasons. In the event that other deviations are not detected, adjustment of the injector is necessary. Let’s start by adjusting the idle speed on the injection engine.

To adjust the idle speed on the injector:

  • Disconnect the battery terminals and dismantle the idle speed controller;
  • Then, the IAC mounting hole is cleaned with compressed air;
  • Now it is possible to disassemble the XX regulator, after which its guide bush is checked. If the sleeve is worn, the element must be changed;
  • Also need to check the needle. Excavation, damage, or other defects are not allowed. If abnormalities are found, the IAC needle should be replaced;
  • Further, with the help of a tester, the regulator windings are checked, if necessary, the contacts are cleaned;
  • At the end of the diagnostic and cleaning process, the device is put back, after which the engine idle and other modes are evaluated.
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We add that a number of problems with idling can occur after cleaning the throttle, which on many cars must be not only properly cleaned, but also trained. If you do not know how to clean and adjust the throttle, we recommend that you read about it in our separate article.

Also note that the injector adjustments and the operation of the power system can be influenced programmatically, that is, by connecting diagnostic equipment with special pre-installed programs to the ECM via the OBD connector. After connecting, you can evaluate many parameters of the engine systems in real time, read, decrypt and reset possible errors.

On the injector, deeper improvements are possible, which involve making a number of changes to the ECU firmware. This procedure is well known under the name chip tuning engine. This setting allows you to change the factory firmware, adapt the control unit to a specific driver and his needs (set the speed of the twentieth, change the fuel cards and affect the mixture formation, ignition, etc.).

What is the result

As you can see, independent improvements and carburetor settings are quite possible in a garage. As for the injector, with its own hands an ordinary car owner without sufficient experience can only check the IAC and clean the device, diagnose some ECM sensors, and also read and reset errors with the OBD2 adapter.

Please note that any attempts at unprofessional interference with the ECU firmware can lead to controller failure or consequences for the engine itself. For this reason, the adjustment and adjustment of the injector should only be in special cases, entrusting the work exclusively to qualified specialists.

Why do I need to clean the throttle? How to clean the throttle, training and adaptation of the throttle after cleaning, useful tips.

Why the engine may have increased idle. The main reasons for the high revolutions of the twentieth on the injection engine and carburetor engines.

The motor stalls at idle: what to check. Possible causes of malfunction on engines with a carburetor, injector, diesel power plants.

Idling "swim" revolutions: why this happens. The main malfunctions associated with idle on a gasoline and diesel engine.

Floating idle engine "to cold". Major malfunctions, symptoms and breakdowns. Unstable idling of the diesel engine.

Causes of vibration and unstable operation of the diesel engine in idle mode. Possible causes and troubleshooting.