How to adjust the idle stroke on the trimmer

How to adjust the carburetor on a STIHL brushcutter

Lawn mowers, like all petrol garden tools, are not difficult to maintain. It is possible and necessary to fix, adjust without the help of others. For example, adjusting the lawn mower’s carburetor with your own hands is a matter of 5 minutes.

Lawn mower carburetor is a part of the power system. In it, as in all carburetors, there is a process of mixing air and fuel (gasoline) for the upcoming supply to the engine cylinders.

In this process, the main thing is the correct proportion of fuel and air, why regulate the carburetor.

Basic carburetor problems and malfunctions.

mesh filter. There are two difficulties with this element more often than not:

To find out the reason of the breakage unscrew fuel filter cover to remove the mesh filter. If it is just a clog, it can be washed in gasoline or purged.

If the strainer is visibly damaged, it is imperative that a new strainer be fitted. There may also be damage to the fuel supply pipe (it is a common practice to check this element during repairs).

In most cases, the carburetor starter mechanism does not work because of clogs. Acetone or the same gasoline should be used for flushing.

Blowing out parts of the clogged carburetor with compressed air is an acceptable and comfortable repair practice.

The throttle body, the linkage of carburetor parts, the inlet or outlet pipe. all these parts are subject to depressurization. You can check probably a simple method. spread soapy foam on the problem area.

The structure of the lawn mower carburetor

Mower carburetor base. duralumin body. A diffuser (a hole with internal contours) is placed in it. This is where the air is forced in. The speed of oxygen (air) flow depends on the cross section (passage opening) of the diffuser.

Fuel ducts in the diffuser. How to adjust the carburettor on a brushcutter. How to adjust the carburettor in practice. video. Fuel is sucked out of them with the help of air flow.

How the carburettor of a lawnmower works

The throttle valve determines the amount of air to be pumped and the engine output depends directly on it.

STIHL FS 55. carburetor adjustment (idle speed)

STIHL FS 55 trimmer for grass in the video to adjust the idle speed.

STIHL FS 55 lawnmower carburettor adjustment

Adjusting the carburetor on a STIHL lawnmower

FS 55 Parts Shop Sadservice.com.ua.

Fuel is sucked into the carburetor system by a pump (pump membrane). Trimmer carburetor Then passes through connector in carburetor. The fluid then flows through the inlet and outlet valves of the pump. Fuel is filtered through the wire mesh. flows through the needle valve into the diaphragm chamber.

• Air supply into the tube with an air baffle (flap). Baffle plate controls the intensity of the air flow.
• The fuel feed system is inevitably narrowed by the mixer to accelerate the flow.
• Gasoline in the float box and restrictor nozzle. The chamber with float regulates temporary volume of petrol. In the float chamber, the pressure level is neutral; in the tube with constriction, the pressure level is already low. Fuel leaks through the nozzle through pressure differential.
• Acceleration of the air stream promotes the fuel (petrol) transfer and atomization. Eventually an air-fuel mixture of required proportion or density appears.
• Air-fuel mixture gets into engine cylinder through fuel pipe.

READ STIHL 250 Carburetor Adjustment Video

The area of the open air damper depends on the level of air density in the system. The more open the choke is, the higher is the fuel consumption and the more power is available.

Simply put, adjusting the carburetor on a chainsaw is about creating good fuel consistency through proper airflow.

How to adjust the carburetor on a lawn mower

Before adjusting, you need to thoroughly clean the filters according to the maintenance in the annotation.

The upcoming adjustment of the lawnmower carburetor with their own hands is made with the adjusting screws. There are three of them:

Right (L). fuel consistency adjustment for low revs.

It is necessary to find the highest idling speed. To do this turn slowly the screw (L) to the right and left.

Turn the screw a quarter of a turn anti-clockwise to adjust the idle speed.

Lower (T). regulates engine at idle speed.

For proper adjustment specifically at idle is typical:

• stable operation of the cool motor;
• Not excessive RPM of a hot motor;
• for the trimmer head is a big stock of revolutions;
• stable engine work with a change of position (sudden raising or lowering of the blade).

READ Carburetor adjustment K 45 on Agro MotoBlock

left (H). adjustment of consistency at high rpm. (The screw should be adjusted last).

left screw (H) is for the general regulation of high revolutions, motor power, temperature and gasoline consumption.

Adjust the lawnmower carburetor with the last screw as follows:

• Open the throttle to the full, in this case give out full throttle. Turn screw clockwise till the revolutions fall down (in this case turn it by ear).
• Turn the screw as slowly as possible counterclockwise until the motor is uneven.
• Then turn back quite a bit, just a little bit to hear the measured, smooth operation.
• For a more enjoyable implementation of the abilities is more convenient to see the work of an experienced user:

Curiously, based on the beliefs of the creator of the video, setting (its correctness) determined by the color of the plug, not only the revs and motor stability.

The correct setting of the carburetor with their own hands in this case. the combustion of fuel consistency without residue, the color of the candle should be light brown.

STIHL FS 55. Adjusting the carburettor (idle speed)

Adjust the STIHL FS 55 grass trimmer carburetor in the video to adjust the idle speed.

Fuel is sucked into the carburetor system by the pump (its diaphragm). Then flows through the nozzle on the carburetor. The fluid then moves through the pump’s inlet and outlet valves. Adjusting and repairing the lawn mower carburetor Grass trimmer stalls at full throttle. STIHL fs 55. Filtered by mesh. Goes through the needle valve into the diaphragm chamber.

• Air supply tube with an air baffle (damper). The air flow is regulated by a partition.
• The fuel supply system is necessarily narrowed by a diffuser to increase the flow rate.
• Gasoline through the float chamber and the nozzle tube with constriction. The float chamber regulates the temporary volume of gasoline. How to start a cold gasoline trimmer for grass STIHL fs-55 correctly. Adjusting the carburetor. In the float chamber, the pressure level is neutral, and in the tube with a constriction is already low. Because of the pressure drop, fuel flows through the nozzle.
• Accelerating air flow helps carry the fuel (gasoline) and atomize it. The air-fuel mixture of the required proportion or density is formed as a result.
• The air-fuel mixture enters the engine cylinder through the fuel pipe.

When a carburetor needs adjustment?

The operator needs to adjust the operation of the working unit in certain cases:

• The new engine has been run-in using 4-5 liters of fuel;
• The fuel composition. brand of engine oil and gasoline. has been changed;
• Weather conditions have changed (winter, summer time);
• The level of air rarefaction has changed;
• The load on the propulsion system has increased;
• After the machine has been stored for an extended period of time;
• The formation of persistent soot on the spark plug;
• The engine immediately stops after starting or does not develop the necessary rpm;
• When vibrating the tuning screws are loosened;
• The amount of fuel consumed has increased;
• No gasoline is pumped into the cylinder;
• there are a lot of tailpipes coming out.

Grass trimmer carburetor adjustment

The initial step in recovery of correct operation of the fuel system is cleaning of the air filter.

Specialists recommend rinsing it in a solution of water and detergents after every 10-15 hours. Direct adjustment of the grass trimmer carburetor is made with three adjustment screws:

• fuel adjustment screw (“L”);
• high speed adjustment screw (“H”);
• Screw responsible for engine idling (“T” or “AT”).

Adjustment of fuel supply at minimum rpm

Before you start tuning the carburetor of a gasoline trimmer, you need to warm the engine up to working temperature.

To do this, start the engine and idle give him to work 10-15 minutes. In the first stage, with the trimmer running, turn the “L” screw slowly until intermittent operation begins or until it stalls. Next, unscrew the screw by ¼ of a turn and check the speed of maximum speed. If the mower quickly and easily reaches high revolutions, this is the most economical mode. In most models on the market, the fuel screw “L” is turned clockwise, but there are grass trimmers where the reduction and increase of mixture is in reverse order.

Grass trimmer idle stroke adjustment

Location of the carburetor adjustment screws

Screw “T” (“AT”) serves as a limiter of reciprocating motion of fuel valve and screwing it increases engine speed, and unscrewing it leads to decreasing speed of crankshaft. Professionals recommend adjusting the lawnmower idle speed screw so that the engine works a little faster at minimum rpm, but the head with the line or blade remains stationary. If after the manipulation it is difficult to start the grass trimmer “from the cold”, it is enough to turn the screw “T” a quarter of a turn and try to start the engine again.

Adjusting the maximum revolution screw of the brushcutter

After restoration of fuel supply at minimum RPM and adjustment of idle speed it is necessary to check stability of operation of the mechanism at higher RPM.

Adjustment of motor at high RPM is performed to protect from overheating and reduce hand fatigue when pressing the gas pedal button. If the engine is working erratically at maximum RPM, turn the “H” screw slowly until smooth and clear running is achieved.

You may need to adjust the throttle trigger (“L”) for optimum RPM when operating the brushcutter.

A gasoline lawn mower, as the name suggests, has an internal combustion engine that uses gasoline as fuel. For it to burn inside, air is needed to form a reaction. The latter creates thermal energy which is then converted into mechanical energy.

To feed the fuel already with air into the engine cylinder and is used by the carburetor.

Idle Speed Adjust. Four Stroke Trimmer

First, the gasoline mixed with oil is transferred to the float chamber. There it continues its flow further, but when the fuel is filled to the desired level, the float rises, shutting off the fuel valve. The primer is a plug that prevents fuel from escaping from the float chamber.

The gasoline passes into the mixing chamber, on top of which air is supplied. The throttle blocks the fuel from entering the cylinder. When the mower pedal is depressed, it opens and the fuel flows in and the engine speeds up. at most the throttle valve can be turned to an angle of 90 degrees, which depends on the force exerted on the gas pedal pedal. A vacuum is created in the mixing chamber, a strong stream of air mixes with the fuel and carries it into the cylinder.

At low speeds, the idle system is used, in which the throttle is not fully opened, but partially.

The carburetor filter cleans the fuel from dust and other small elements, protecting the jets from their harmful effects. If they are clogged, however, the motor’s power will be noticeably reduced.

The task of the carburetor is to quickly send the fuel to the cylinder with air, mix it with oxygen, which allows the gasoline to burn. The difference between the car carburetor and the trimmer is only in the presence of a membrane in the latter, which is used for sucking gasoline from the tank.

Adjusting the Husqvarna carburetor

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

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

Note: If you adjust the 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 trimmer head with cord of 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 on 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 turning at idle speed, turn the idle speed screw, t.е. lower one, must be turned counterclockwise until the trimmer head stops rotating). Carefully turn both needles (right and left) to a central position between fully unscrewed and fully screwed in (do not twist behind the stopper)!, this may cause the Husqvarna engine to break).

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

1) Right L screw. adjusts low RPM mixture enrichment (adjusts first): Find maximum idle speed by slowly turning right and left. Then turn the screw ¼ turn counterclockwise. Note: From the Husqvarna factory, the right screw was turned all the way out (0.5 turns). It is now looking at 11 o’clock. 2) Bottom screw T. Husqvarna idle speed adjustment (if needed): turns screw clockwise to increase idle speed, counterclockwise to decrease it.

It is considered correct to adjust the idle speed when:

• A cold engine is idling steadily.
• A hot engine does not have too high idle RPMs.
• Allow enough revolutions until the trimmer head starts to rotate.
• The motor runs steadily in any position (for example, when the blade is lowered sharply).

Note: From the factory (Husqvarna) the idle screw was turned to 8 full turns and 2 hours (it still is). Recommended idle speed for Husqvarna lawn mower is 2.900 rpm. 3) Left H screw. adjusts high RPM mixture enrichment (adjusts last). It regulates maximum RPM, engine power, temperature and fuel consumption.

Note: The 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 engine begins to run rough.
• Then turn the screw slowly back a short distance clockwise until the Husqvarna engine begins to run smoothly.

This concludes the Husqvarna adjustment.

Note: Recommended maximum Husqvarna engine rpm 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 factory (Husqvarna) the left screw was completely unscrewed (0.5 turns) and blocked (filled in) with hard plastic, which I drilled out after the warranty expired. Right now the left screw (as well as the right screw) is looking at about 11 o’clock.

Checking that the Husqvarna carburetor is set correctly

Engine quickly, smoothly and steadily picks up speed, and slightly even at maximum speed, the trimmer head T-35 at idle should not rotate.