How to Adjust a Lawn Mower Valve

This article describes the adjustment of the tiller, namely its main parts: carburetor, valves and fuel system. The process is not easy, so we also attached some photos and videos.

Tiller carburetor adjustment

The instability of the revs of the tiller engine indicates that the carburetor needs to be adjusted. The need to perform this procedure, as a rule, arises before the start of the agricultural season, when the equipment has not been used for a long time, or after it, when the tiller has been subjected to significant loads for a long period of time.
Before starting the adjustment, it is necessary to warm up the engine. The actual work process is as follows:

How to Adjust a Lawn Mower Valve

  • The screws regulating the small and maximum gas are fully screwed in, after which they loosen by about one and a half turns.
  • The motor starts and warms up for about 10 minutes.
  • The lever that controls the power plant should be set to its minimum position, but the motor should not stop.
  • The screw adjusting the throttle shutter will help to adjust the minimum idle speed so that the motor operation is stable, without extraneous noise and stops.
  • The rotation of the screws makes it possible to precisely determine the amount of combustible mixture that enters the motor.
  • Tightening the screw helps to enrich the mixture, while unscrewing it, on the contrary, increases the amount of air entering the engine;

Use the idle screw to adjust the maximum idle speed. The same should be done with minimal speed, using the throttle stop screw. The essence of this adjustment is that the screw of the flap allows you to adjust the angle at which it is closed;

The lever responsible for controlling the engine should be moved to the “gas” position. If the operation of the tiller still cannot be called stable, the full throttle screw is adjusted until the ideal stroke is observed. However, the maximum allowable screw speed is 2.5.

The carburetor adjustment accuracy can also be determined by how the spark plug looks after a short work under load. If the working mixture is perfect, then there will be no soot or traces of fuel on the candle that indicate too lean, or, conversely, too rich a combustible mixture. It should be noted, however, that carbon deposits or traces of fuel on a candle can speak not only about incorrect adjustment, but also about more serious problems of the tiller, including faulty ignition or cooling system.

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Tiller valve clearance adjustment

Over time, under significant loads, the valve clearance of the tiller engine changes. The reason for this may be the wear of parts. Insufficient distance leads to the fact that the gas distribution stages change significantly, as a result of which it is not possible to achieve a sufficient degree of compression, the power plant operates intermittently and does not reach the declared power. In especially serious situations, even valve deformation can be observed. If the gap is too large, significant mechanical noises are recorded, the gas distribution phases also change significantly, the valves open for too short a time, due to which the cylinder does not fill properly, power drops, and failures occur. Clearance adjustment is necessary as soon as the engine has become incorrect or occur with significant noise. Ideally, the engine being adjusted should be cool.

So, first you need to get to the flywheel. It is on this detail that the top dead center value is noted. The flywheel is hidden under the cover, and therefore have to remove it. Before removal of a casing the oil bath of the air filter is removed. To facilitate the task in the process of removing the casing, you can fix all the latches with rubber bands. The key unscrews all bolted connections, after which the lid can be removed without problems.

Video: How to Adjust a Lawn Mower Valve


On the flywheel, you can see the marks that mark TDC, as well as the values ​​of 5, 10 and 20 degrees. A mark of 20 degrees indicates the injection of a combustible mixture. The flywheel should be brought under the top dead center, focusing on the appropriate division. The valve cover is untwisted and removed.

In the process of adjustment you need to use the following tools:

  • Screwdriver;
  • Ring spanner for 10;
  • The blade is 0.1 mm thick.

According to the technical data sheet, the valve clearance of the tiller engine is from 0.1 to 0.15 millimeters, and therefore, with the help of a blade, it can be adjusted very precisely. However, you need to pay attention to the fact that some blades have a thickness of 0.8 mm, which is unacceptable. The exact value can be found with a micrometer or from information on the manufacturer’s website. The adjustment is as follows:

  • Screwdriver;
  • We relax the nut, insert the blade and begin to tighten;
  • It should be guided by the blade, gently tightening the nut;
  • Adjustment is carried out until the valve free play is eliminated. He should sit tight enough.
  • In the reverse order, we assemble the casing, install the oil bath in place.
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If all the manipulations were carried out without errors, then the engine will work smoothly and without unnecessary noise.

Tiller fuel system adjustment

If fuel is not supplied to the cylinder, then, first of all, it is necessary to check whether there is enough fuel in the tank. It is also necessary to check whether it goes to the carburetor. To do this, a hose is removed from the inlet fitting of the device. If we are talking about a carburetor type K45, you should press on its quencher so that the fuel begins to pour out through the drainage hole.

If fuel does not enter the carburetor, you need to turn off the fuel supply valve, completely disassemble it and remove accumulated dirt from the mechanical filter. To achieve maximum purity, all components must be treated with gasoline. The fuel valve is assembled and returned to its original place.

If the fuel enters the carburetor, but is not supplied to the cylinders, it is necessary to check the correct operation of the fuel valve, as well as the presence of dirt on the nozzles.

To deal with the carburetor of a gasoline tiller type KMB-5, you must remove it from the engine and pour fuel from the float chamber. Through the fitting (see the figure), with which gas is supplied, it is necessary to supply the air mixture, having previously set the carburetor in the working position. The passage of air should go unhindered, and when the carburetor is overturned, it should completely stop. These features indicate that the part is fully operational.

Fig. 2. Carburetor KMB-5

Details in the figure: 1. nozzle supplying fuel; 2. upper case; 3. throttle valve; 4. small gas needle; 5. jet; 6. lower case; 7. air damper; 8. screw securing the screed; 9. needle maximum gas; 10. spray element; 11. a float; 12. fuel supply valve.

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The fuel level inside the float chamber can be adjusted using the float tab. Ideally, it should range from 3 to 3.5 centimeters.

To purge the nozzles, it is necessary to unscrew the screws responsible for the full and low gas.
Cleaning carburetor parts begins by loosening the screws holding the upper housing. The lower case is removed, the fuel supply valve is flushed with gasoline, and the dirt from the nozzles is blown out by the pump. It is necessary to check whether the float is intact. It is strictly forbidden to use rags in the cleaning process.

After cleaning, the cases are connected. It must be ensured that the spray tube passes clearly into the hole located on the upper housing. Open the throttle body and check how well the assembly is completed. The screws securing the upper case tightly tighten. After the assembly process is fully completed, you should adjust the carburetor. This will significantly improve the performance of the tiller with attachments, as for the correct operation requires perfect tuning of all its parts.

If the carburetor DM 1.08.100 is installed on the engine of the tiller, then the procedure for its adjustment will be as follows:

  • It is necessary to tighten the screw 10 (Fig. 3) of small gas to the full stop and unscrew it half a turn from itself.
  • Then you need to tighten the screw 9 full gas completely unscrew it by 2 turns.
  • Loosen screw 4 (Fig. 4) of the minimum engine speed right up to the lever stop in the tide of the carburetor body and turn it 2 turns.
  • Start the tiller engine, then adjust the stable operation at maximum speed after warming up with screw 9.

Do not let the engine control lever turn off, set it to the minimum gas position (revolutions) and set the idle speed at a stable speed by loosening screw 10.

Fig. 3. Carburetor DM 1.08.100

Fig. 4. DM carburetor outside

That’s basically it. Highlights of the adjustment of the main parts of the tiller are considered. Adjust your tiller with pleasure!