Frequent malfunctions of the Husqvarna 128R grass trimmer

There are many problems, which can be solved by adjusting carburetor. Adjusting the carburetor on your Husqvarna chain saw is necessary if you experience problems such as:

  • increased idle speed;
  • Heavy smoking during tool operation;
  • Difficulty starting a cold or hot engine
  • Lack of traction and reduced maximum rpm.

This is by no means a complete list of problems, the solution of which can become a carburetor tuning Husqvarna. In a number of cases, adjustment of the quality and quantity of the fuel mixture is carried out after an engine overhaul or during a scheduled maintenance of the chainsaw.

Husqvarna recommends adjusting the carburetor before and after the break-in period.

Adjusting the Husqvarna carburetor

Before adjusting the Husqvarna, do maintenance on the grass trimmer (wash the mower and engine, replace the spark plug, repair minor defects).

Be sure to wash the foam element of the air filter. Wash element with soap and warm water, then wring and dry it (or replace it if it is old or damaged).

Note: If you adjust your Husqvarna carburetor with a dirty air filter, after cleaning the air filter the fuel mixture will become much leaner (which can lead to poor performance or even engine failure). Install a trimmer head with a cord of the maximum allowable diameter and standard length (up to the cutting blade in the extra guard) to put stress on the engine while adjusting the high RPM screw of the Husqvarna carburetor. Start the machine according to the Husqvarna Operator’s Manual and allow it to warm up for 10 minutes (if the trimmer head is still turning at idle speed, the idle speed screw, i.e.е. lower screw should be turned counterclockwise until the trimmer head stops rotating). Carefully turn both needles (right and left) to a middle position between fully unscrewed and fully screwed in (do not turn by the stopper!, it may cause the Husqvarna engine to malfunction).

There are three adjustment screws for adjusting the Husqvarna carburetor: right, left, and bottom.

1) Right L screw controls low mixture enrichment (first to adjust): Find maximum idle speed by slowly turning right and left. Then turn this screw ¼ turn counterclockwise. Note: From the Husqvarna factory, the right screw has been turned all the way out (0.5 turn). It is now looking at “11 o’clock.”. 2) Bottom screw T. Husqvarna engine idle speed adjustment (if needed): turning it clockwise increases idle speed, counterclockwise reduces it.

It is considered proper to adjust the idle speed when:

A hot engine does not run too fast at idle speed.

Note: From the factory (Husqvarna) the idle speed screw was turned to 8 full rpm and “2 o’clock” (now it stays that way). Recommended idle speed for Husqvarna mowers is 2.900 rpm. 3) Left H screw. adjusts high RPM mixture enrichment (last to be adjusted). It controls maximum rpm, engine power, temperature, and fuel consumption.

Note: Husqvarna engine should not run at full speed for more than 10 seconds!

  • Open the throttle fully (give full throttle) and slowly turn the left screw clockwise until the Husqvarna engine RPM is reduced (by ear).
  • Then turn the left screw very slowly counterclockwise until the motor begins to run unevenly.
  • Then turn the screw slowly back a short distance clockwise until the Husqvarna engine is running smoothly.

This completes the adjustment of the Husqvarna.

Note: Recommended maximum rpm for the Husqvarna is 11.500 rpm. The maximum power output of the Husqvarna 333R lawnmower engine is 1.6 kW (2.1 л.с.) at 8.400 rpm.

Note: On a new Husqvarna trimmer from the manufacturer (Husqvarna) the left screw was completely unscrewed (0.5 turn) and blocked (filled) with hard plastic, which I drilled out after the warranty expired. Now the left screw (as well as the right one) is looking at approximately “11 o’clock”.

Checking the correct setting of the Husqvarna carburetor

The engine quickly, smoothly and confidently picks up speed, and a little chetverit at maximum speed, the trimmer head T-35 at idle should not rotate.

Getting the carburetor to adjust

Module configuration is not repairable, and replacement is not required. Honda Carburetor Cleaning the carburetor. In this case, the carburetor repair kit for the gas grass trimmer is not required.

  • L. is initially adjusted because it is responsible for fuel delivery at low speeds;
  • N. Is responsible for the supply of gasoline at high speeds, as well as fuel consumption and temperature;
  • T. It makes a simple adjustment.

There are variations, usually a Chinese gasoline scraper carburetor, where there is only one screw on the body to adjust. to adjust the idle speed. This does not mean that the module adjusts automatically. This means that it will be difficult to perform even this type of repair as a debugging. The photo shows the adjustment of a Chinese gasoline carburetor.

  • The module is adjusted only when the engine is warmed up: to do this, the device is first turned on for 10 minutes. Adjusting the carburetor If the mower head is idling, begin adjustment immediately: turn the T screw counterclockwise until it stops turning.
  • Adjustment begins with the L screw. The screw rotates left and right until it finds its position at which the idle speed becomes maximum.
  • Then turn the screw and turn it anticlockwise. This will be its working position.
  • The idle speed should be adjusted by turning counterclockwise to increase the speed, and clockwise. reduce. Its adjustment is to reach a mode in which sufficient rotation is carried out before the mower starts to rotate. The motor should then run stably in various positions.
  • The position of the L screw is determined last. at maximum speeds, the grass trimmer should not run for more than 10 seconds. Throttle opens, screw rotates clockwise, very slowly, until the rotation speed is reduced to the level of the ear.
  • Then the screw also turns slowly counterclockwise until the engine fails. Then the screw is turned back clockwise until the engine restarts normally.

We suggest reading Shoes for Extremely Low Temperatures If you have a tonometer and if the product’s data sheet specifies the recommended speed, the correction can be made more accurate by focusing on the readings of the device rather than the ear.

Please explain. In the adjusting section of item 5, the L L screw? Should I read screw A? Thank you

Tell me the initial position of the screws H L LA

Tell me the initial position of the screws H L LA

HOW TO SET THE CARBUITER On A STIHL CHIEF PARAMETER. How to adjust your chainsaw carburetor correctly

A chainsaw is a technically complex tool that needs maintenance from time to time. Cleaning, filter change and of course adjustment of your chainsaw carburetor will help to last the whole time it is needed. In this article we will look at carburetor tuning. How and why it is carried out.

Situations in which adjustment is necessary

New chain saws are shipped from the manufacturer with already repaired carburetors. This is called standard adjustment. But for the normal passage of the process is required to reduce the maximum engine speed, to adjust the carburetor. After running-in, the chainsaw needs fine-tuning to achieve maximum engine performance.

Also a strong signal for cleaning and adjusting is increased fuel consumption that is detrimental to the exhaust system. Simply put, the chainsaw begins to smoke heavily and the muffler becomes clogged with carbon deposits, which in turn will lead to reduced power. If there is not enough fuel in the mixture, the engine parts do not lubricate properly and wear out prematurely. Also, a poor mixture can cause the engine to seize up due to overheating (this is one reason why).

Adjustment is necessary in the case when the engine does not hold idle speed, stalls or does not develop full power.

carburetor adjustment must be done with clean air and fuel filters.


Proper adjustment of the chainsaw carburetor should take place with a special tool. a tachometer. It allows you to most accurately determine the maximum number of engine revolutions and adjust them according to the manufacturer’s requirements. It is necessary to have a small slotted screwdriver for adjustment. Some chainsaw models need a special adjustment wrench, without which it is impossible to work.

The key for adjusting certain carburettor models is available only at service centers authorized by the manufacturer for chainsaw repair. This measure is aimed at reducing breakdowns due to improper adjustment by inexperienced users and those who are engaged in repair, not having official permission to do so.

If possible, have your chainsaw checked by an authorized service center that has been certified by the manufacturer.

How the carburetor is tuned

The adjustment procedure is fairly straightforward and consists of the following steps:

  • Adjusting the engine for smooth operation at low rpm.
  • Adjusting the carburetor for proper fuel mixture at maximum rpm.
  • Fine-tuning the carburetor for no-load operation.
  • Checking the chainsaw in all modes.

Adjustment of the carburetor should be carried out after the engine has worked a little and warmed up.

Now we will consider how the correct adjustment of the carburetor of a chainsaw in more detail. Virtually all carburetor models have three adjustment screws. Screw (T) adjusts for fine-tuning at idle speed. Screw (H) adjusts for maximum rpm. The screw (L) regulates the formation of the mixture at low rpm. Tightening the screws (L) and (H) depletes the fuel supply and the mixture and respectively increases the rpm.

Process description

If the carburetor is out of adjustment and the chainsaw cannot be started, start the adjustment by turning the screws (L) and (H) into the standard setting. this is 1/5 of a turn of the screws until they are completely screwed in. After that, it is necessary to start the engine, let it run for a while and warm up. The next stage is adjustment of low revolution mode. Optimal work of the engine at low revolutions is achieved by adjusting the propeller (L) and idling (T). To do this, first turn the screw (L) until the maximum engine rpm is reached, then release it by 1/4 and use the screw (T) to set the idle speed to normal.

After adjusting the RPM and RPM at a low speed, adjust the traction and the maximum engine RPM. To do this, slowly tighten the screw (H) and by the reading of the electronic tachometer check the revolutions.

it is not allowed to exceed the maximum engine speed declared by the manufacturer.

An important step is to check the saw on all modes of operation after its adjustment, for this you need to let the chainsaw cool down, then start it according to the algorithm of starting a cold tool. If the saw starts normally and runs smoothly at idle, you need to check how it saws. If you find any defects in your chainsaw’s power, check the throttle retightening screw (H) and see if the throttle retightening is working.

Loss of traction at the maximum rpm recommended by the manufacturer is an indication of a worn cylinder or poor fuel quality.

Adjusting the carburetor on a Chinese chainsaw

The carburetors on Chinese-made saws are made in the same way as European-made saws and have the same adjustment screws.

Adjustment of the chainsaw carburetor

The carburetors on most chainsaws have three screws for adjustment:

  • L. screw for low rpm adjustment
  • H. high speed adjustment nipple screw
  • T (LA) screw on the Partner and Husqvarna (Stihl has LA). adjustment of the chain saw’s idle speed

H and L screws are used to adjust mixture ratio of petrol and air, which is determined by opening of carburettor choke. Unscrewing the screws enriches the fuel mixture and rpm increases correspondingly, tightening the screws depletes the fuel mixture and the rpm drops.

adjusting, carburetor, husqvarna, brushcutter

The T(LA) screw is for adjusting the no-load speed. The basic tuning of the chainsaw is done at the factory during the final test. The carburetor is usually set for a richer (than optimal) fuel mixture. The factory setting has to be kept for the first few hours of operation. Then (optional) the carburetor is adjusted more accurately.

Read also: What is a thickness gauge for?

begin with the idle speed setting, turning the T (LA) screw counterclockwise until the chain stops completely at a steady engine rpm.

For further fine adjustment you need a tachometer and it is better to entrust it to specialists. and moreover in most cases it may not be necessary.

Start with the L screw, then use the H screw and finally the T screw (LA).

Find the highest idle speed by slowly turning the L screw in different directions. After finding the position of the highest engine revolutions, you need to turn the screw L for 1/4 turn counterclockwise. If the chain is idling, turn the screw T clockwise until it stops.

The H screw is used to adjust the power and speed. Adjusting the carburetor to a lean mixture leads to excessive RPM, overheating of the engine and damage to the chainsaw piston.

Warm up the chainsaw engine at idle for at least 10 seconds and turn the H screw 1/4 turn counterclockwise. let the engine run for about 10 seconds. then check the maximum rpm with a tachometer. If the maximum rpm is not what it should be, repeat the operation. If the mixture is too rich, the muffler starts to smoke and if the mixture is too lean, the saw starts to squeal and overheat.

Finish the adjustment by adjusting the idle speed, as already described above. The idle speed is set correctly if the engine runs smoothly at minimum rpm and the chain does not rotate.

The carburetor may be considered regulated if the engine accelerates fast and sounds like a four-stroke at full throttle.

The carburetor in a chainsaw is needed to mix and deliver fuel to the combustion chamber of the engine. If the carburetor is adjusted correctly, the operation of the equipment will be reliable in all modes and the fuel consumption will be economical. In general this rule applies to all internal combustion engines.

How a lawn mower carburetor works

The throttle valve determines the amount of air to be dispensed, and the engine output depends directly on this.

Fuel is sucked into the carburetor system by the pump (its diaphragm). Then goes through the nozzle in the carburetor. Then the fluid moves through the inlet and outlet valves of the pump. Is filtered out by the mesh. Moves through the needle valve into the diaphragm chamber.

  • The air is sucked in by a tube with an air baffle (damper). Baffle plate regulates the intensity of the air flow.
  • The fuel system is necessarily narrowed by a diffuser to increase the rate of flow.
  • Gasoline through the float chamber and restrictor tube. The float chamber controls the temporary volume of gasoline. In the float chamber, the pressure level is neutral, but in the tube with a constriction, the pressure level is already low. Because of the differential pressure, the fuel flows through the nozzle.
  • Accelerating the airflow helps carry the fuel (gasoline) and atomize it. The result is an air-fuel mixture of the desired proportion or density.
  • The air-fuel mixture enters the engine cylinder through the fuel tube.

The area of the open air damper depends on the level of air density in the system. The wider the damper is open, the greater the fuel consumption and power.

Simply put, the adjustment of the carburetor on the gasoline mower. the creation of an optimal fuel mixture at the expense of the correct air supply.

Adjusting the carburetor on the Husqvarna 128R lawn mower.

The first question worth answering in a review of the header topic is Why you need to adjust the carburetor of the 128R grass mower? It is all about European fuel standards. 128R lawnmower is adjusted for fuel standards of the European Union. We have a lower quality fuel (we discuss gasoline AI-92), which causes the need for the given adjustment. The procedure of adjusting the Husqvarna 128R carburetor is not complicated. What you need for its production. a tachometer of revolutions, adjusting screwdrivers.

We set the line out of the trimmer head to 15 cm on each side (this essentially affects the revolutions).

Dilute gasoline AI-92 with Husqvarna two-stroke engine oil in proportion 1:50 (one part oil to 50 parts gasoline). For ease of calculation we recommend the ratio. per 1 liter of fuel x 20 milliliters of oil. For the first start of the brush cutter we recommend to choose the ratio: 1 liter of fuel x 23 ml of oil (this ratio is for the first run-in of the engine). The exact observance of these ratios and using only Husqvarna oil for two-stroke engines is a guarantee of the engine durability and warranty obligation fulfillment by the supplier in case of a guarantee case.

Start the mower and turn throttle up to full throttle

rpm. Use the right adjusting screw H to adjust the RPM to between 8,500 and 8,800 on the tachometer.

Release throttle. At idle on top of the carburetor adjusting screw T adjusts idle speed to the level of 3000-3200 on the tachometer. The engine should run smoothly, without flinching. The trimmer head should stop turning.

If you notice visible smokiness from the exhaust fumes or unstable idle speed with the idle speed set, adjust the “quality of mixture” with the carburetor’s left adjuster screw L.

Having trouble adjusting the carburetor on your Husqvarna 128R?. Bring it to our service center. we’ll help you.

The practice of Husqvarna gasoline tool service at our service center showed that the adjustment is needed from time to time on other models of Husqvarna chain saws and brushcutters as well. These adjustments, similar to the method described for adjusting the carburetor of Husqvarna 128R lawnmower, can be made by any user. Below, by way of reference, we give motor speed figures for different equipment and in different modes.

From personal experience

lawnmower or grass trimmer

grass trimmer is a broader concept than a lawnmower (lawn mower), as it can also be electric. Gasoline grass trimmer and lawnmower. is the same.

Some authors assure that the grass trimmer. is a weaker tool as opposed to a more powerful lawn trimmer, which can be used to mow shrubs. Personally, I have a tool with a maximum power of 1.7 kW and capable, as stated in the instructions, to mow small bushes up to 10 mm thick. The user guide is called “gasoline grass trimmer. “.

Fuel mix proportion

I read somewhere that if the lawnmower manual and the oil can indicated different proportions of fuel mixture, you should use the proportion indicated in the manual.

For a long time that’s what I did. the oil surplus was dripping from the engine onto the gas tank, and the plug constantly got soot on it, because the manual said that the ratio was 1:25 for a running-in engine, and the canister. 1:50. After switching to a 1:50 ratio, oil leakage is stopped. The spark plug continued to burn, but with less intensity (carburetor was not yet adjusted).

Still some users of gasoline tools determine the proportion of the fuel mixture “by eye”. If during the mixing the amount of oil will be reduced, after a while you may hear some unusual noise immediately after starting the engine, but it will disappear gradually during the warm-up, and the engine will stop with a sharp jerk. Continued operation of the grass trimmer in this mode will lead to its failure.

Cleaning the spark plug

In the worst times of the trimmer with an unadjusted carburetor, the engine would stop starting after using every tank of fuel. And only after the spark plug had been cleaned of the fouling was it possible to continue working.

Fine sandpaper was used to clean the electrodes, and to clean the space between the insulator and the body. A thin paper clip with a bent end. First, the electrodes were wiped of a lot of dirt with a rag, then they were sanded with sandpaper. After that the plug was immersed in diesel fuel and the soaked plug was scraped with a paper clip from the surfaces of the insulator, the body interior and between them. Then the spark plug was several times lowered into the diesel fuel and the soiling was scrubbed off. Occasionally, the cleaning procedure with a paperclip and flushing was repeated. After that, the plug was wiped dry and ready for further use.

Incredibly, with an unadjusted carburetor, one can use up a tank of fuel mixture in less than 10 minutes. tested in practice, when the grass trimmer was started and operated at high rpm with maximum fuel flow (the adjustment screw was unscrewed much more than the norm).

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