Why the grass trimmer eats a lot of gasoline.

Design and adjustment of the carburetor on chain saws and trimmers

lawnmower or grass trimmer with an internal combustion engine requires not only constant refilling of the fuel mixture of gasoline and oil, but also periodic adjustment of this fuel. The carburetor is responsible for the fuel supply to the lawnmower cylinder, the efficiency and productivity of the tool depends on the proper operation of the carburetor. If in the process of operation is detected malfunction (abnormal) operation of the engine, the first thing to do is to adjust the carburetor of the lawnmower. Before adjusting the carburetor of the gasoline trimmer for grass, let’s first understand its design.

Lawnmowers are equipped with internal combustion engines of the two-stroke type. To supply the air-fuel mixture into the engine cylinder, the carburetor is used. In the design of gasoline units. this is a key element, without which the work of the internal combustion engine is not possible. And this carburetor differs from the car device not only in size, but also in the principle of operation. In particular, this difference lies in the presence of a diaphragm, which plays the role of a gasoline pump. It is due to the presence of the diaphragm, the devices under consideration in the design of two-stroke internal combustion engines are called diaphragm.

The whole mechanism is designed as a small piece with channels, valves and diaphragms inside. The carburetor body is made of aluminum, and the internal structure is shown in the photo below.

Before the adjustment of the lawnmower carburetor with your own hands, it is necessary to understand all the constituent elements of the device in question. The carburetor on your lawnmower and grass trimmer consists of the following parts:

grass, trimmer, gasoline
  • Diffuser or Venturi nozzle. through this nozzle air is sucked into the system
  • Air damper. opens and closes the supply of filtered air
  • Fuel channel of maximum rpm
  • Fuel channels (nozzles) idling idle and medium speed
  • Throttle valve. the amount of opening is regulated by throttle pressure
  • Impulse channel nozzle. connects to the internal crankcase channel of the engine
  • Fuel inlet port (2). provides fuel supply from the fuel tank
  • Diaphragm (4). is responsible for sucking fuel from the gas tank
  • Fuel suction valve from tank (3)
  • Fuel valve in the carburetor channel (5)
  • Fuel filter element (6) or fine fuel filter
  • Fuel line (10)
  • needle of the needle valve (14). is responsible for supplying fuel into the diaphragm chamber
  • chamber. fuel mixture that is fed to the cylinder through nozzles and throttle valve
  • Control diaphragm (18). manual fuel primer is provided
  • Lever connected to diaphragm (17)
  • Idle speed adjustment screw (15)
  • Fuel quantity adjustment screw, supplied to the diffuser (13)

Having an idea of how the carburetor is built inside, it is necessary to understand the principle of its operation. A detailed description of how the carburetor on a two-stroke internal combustion engine works, using a chainsaw as an example, is described in this material.

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Instructions for operating the carburetor

The gasoline that goes into this device must not contain mechanical impurities. Treat all parts only with gasoline. Do not use thinner, because it damages the elasticity of the washer and rubber parts.

Blow through with compressed air to dry out parts. Do not use a wire or needle to clean the small holes. Installation after repair or cleaning should be carried out moderately to prevent the twisting and deformation of parts.

The float chamber must be connected to the housing hermetically. Check the air filter connection prior to operation. There must not be any gasoline leaks.

Before starting the engine, prepare the carburettor. Make sure there is no petrol leaking from it. To do this, open the fuel cock. Close the choke and turn the control lever to the stop. Open the choke to 1/8 1/4 of its maximum stroke.

If the air temperature is low (below 5o C), squeeze the dome until fuel appears from the hole.

During start slightly open the choke, and after the engine warms up fully open the choke.

Repair of K-45: basic recommendations,

To repair the carburetor with your own hands, we suggest you read about repairing the motor block Neva MB-2.

  • If there is excess air in the internal combustion chamber. Try to change the gasket between the head and the carburetor and tighten the mounting nuts at the connection. If it has not helped, the cause may be the wear of the shaft on the slide or hole, where it is connected. Such a shaft is subject to replacement, and in the case of broken holes the device is changed completely.
  • When there is a lot of fuel coming into the float chamber. In this case check and replace worn parts: float, nozzles, needle.
  • If there is not much gasoline in the carburetor, check the filter and sump, fuel hoses and gas tank. Dirty parts should be washed or changed and if the tank is corroded from inside you have to clean it with caustic soda.
  • If an increase in fuel consumption is noticed, adjust the carburettor by referring to the user manual.

Lawnmower carburettor components

The carburetor of a lawnmower is based on an aluminum housing. There is a diffuser (orifice with internal circuits). The air is pumped through this port. Oxygen (air) flow rate depends on diffuser cross-section (orifice).

The diffuser is equipped with fuel channels. From them, the fuel is drawn in by a flow of air.

Adjusting the brushcutter carburetor in practice

You can buy brushcutter carburetors here: How to adjust the carburetor if it is adjusted.

The numbers mean this: one part oil, fifty parts petrol. From here: 1000 ml (1 liter of gasoline) divided by 50, we get 20 ml, that is 1:50.

In this way it is possible to calculate the composition of the fuel mixture (gasoline/oil) in any proportions. To add oil to gasoline without “by eye”, it is advisable to take a 20 ml syringe of medicine, fill it with oil and “inject” it into a container to prepare fuel mixture.

The small amount of oil in the engine oil mix leads to increased wear of the cylinder and piston groups. Too much oil in the mixture, although not so fatal, but also harmful. Piston rings may get corked, combustion chamber sooting may occur, engine power may drop. The muffler screen can get blocked. Therefore, some users (after the expiration of the warranty period on the grass trimmer) recommend that it be dismantled.

The gasoline used in the brushcutter is AI 92. You must read the exact gasoline brand in the instruction manual. It is not worth trying to “force” the engine by filling it with 95th gasoline. This can lead to overheating, unstable operation of the trimmer for grass and breakage.

It is not recommended to leave fuel in the trimmer‘s tank for long pauses in work. It is best to finish the day’s work with all the mixture out. If you don’t do that, then, since the gasoline will evaporate from the engine during the night and a thin film of oil will remain, the carburetor jets may get clogged. This will cause difficulties the next time you start the engine.

It is also necessary to follow the safety rules when storing fuel. Many people pour gasoline into a plastic water bottle. Is it worth doing it that way??

Instructions for cleaning a brushcutter carburetor: the quick way

Many people prefer to use the quick method of flushing the lawnmower carburetor. This method is effective in the case when single faults of the device are identified. Consider step by step how the process of disassembly and cleaning with your own hands:

After cleaning the carburettor with compressed air, do not rush to put it on the brushcutter. Now you can check if it is working properly, or to be more precise, how it pumps fuel. To do this, connect the hoses to the lead connections.

Dip the feeding hose into a can of gasoline, and pump the primer.

If gasoline will flow from the return, it means that the work on cleaning the carburetor was done successfully. Now you can install the part on the mower and check the function of the tool. This completes the process of cleaning the product quickly. All cleaning procedure is presented in detail on the video

Muffler its clogging and impossibility to start the gasoline trimmer

What else can be the reason that it is impossible to start the engine of the gasoline trimmer? Even before resorting to more drastic actions, you should check the serviceability of the muffler or exhaust duct. This does not apply to new trimmers, which have almost no particular depletion. If the trimmer is many years old and the tool has not been subjected to diagnostic measures, the muffler should be checked for clogging.

If the muffler of the lawnmower is clogged, the exhaust gases have nowhere to go, and therefore the engine cannot be started. In the blink of an eye, the exhaust port can not be clogged, so the day before, such signs should have been manifested:

  • Increased sound of engine operation, which is associated with overcoming a lot of resistance by exhaust gases to release them
  • Black smoke from the muffler. soot, which is deposited on the walls of the exhaust system
  • Unstable operation of the engine
  • The engine stops on its own when running at idle speed

You can exclude or confirm this factor by examining the exhaust system. If the anti-sparking grid has significant clogging, then undoubtedly the cause of the inability to start the engine is in the exhaust duct. It is necessary to clean the mesh, but do it carefully, because black sludge is a very dangerous carcinogen, which can provoke serious diseases of the human respiratory system. To clean the anti-spark net and the walls of the grass trimmer muffler, use special agents, and work with the use of protective equipment.

Grass trimmer carburetor: tuning, adjustment with your own hands

On trimmers, in addition to electric motors, gasoline internal combustion engines are installed. This mechanism requires special attention to itself, because if it is not properly adjusted, it will either refuse to work, or will work with interruptions and loss of power. Basically, the adjustment of the engine is to adjust the fuel supply, and this is done with the grass trimmer carburetor.

Fuel expert: when buying fuel for your lawnmower, give preference to 98 gasoline

When using 95 motor gasoline, it is important to remember that this fuel should not be kept in cans for long periods of time. If you do need gasoline for your lawn mower, it’s better to use 98.

“95 motor gasoline is meant for driving, not idling cars. If you fill the tank at least once a month, you can use it with no worries. provided, of course, that the producer has also approved the use of 95 gasoline,” says Urmas Kuuse, wholesale manager of Neste Eesti.

Husqvarna trimmer fuel line and carb rebuild

“In summer, people often stock up on fuel for lawn mowers and other garden equipment. so they always have it handy. In private households, not much fuel is used and often not enough is spent.

But gasoline which has been in contact with the air longer than the prescribed 95% can create problems for the engine,” said the fuel expert.

Urmas Kuuse advises not to use gasoline that has been stored for more than one month at home: “Gasoline stored in a can inevitably comes into contact with air and if ethanol in the motor gasoline is up to 10 per cent, there is a high probability that water condenses in the fuel. The danger is less in case of 98 petrol, where the permitted ethanol content is up to 5 per cent”.

Ethanol in motor gasoline increases the octane rating. It adds power to the engine and reduces fuel consumption.

Ethanol is one of the best known components of motor gasoline. Alternatively tert-butyl methyl ether (MTBE) is used as an oxygen component, but from an environmental standpoint ethanol is a better choice.

Alkylbenzene, which is specially produced for 2 and 4-stroke engines, does not contain any additives. This gasoline for small engines is sold in garden and construction stores in 5-liter cans, and has an even longer shelf life of three years.

Neste (NESTE, Nasdaq stock exchange in Helsinki) creates and develops environmentally friendly solutions based on the needs of transport as well as its business and private customers. Our products made from renewable raw materials enable environmentally conscious customers to reduce their carbon footprint. Our portfolio also includes high-quality solutions for aviation and plastics. Neste is one of the world’s largest producers of diesel fuel from renewable raw materials. We aim to be a reliable partner whose knowledge is based on extensive scientific research and which uses environmentally friendly production processes. Neste generated 15.8 billion euros in sales revenue in 2019. Neste was named the third most environmentally friendly major company in the Global100 rating in 2020. Neste has operated in Estonia since 1989.

How to adjust the carburetor on a lawn mower

Before adjusting, it is necessary to thoroughly clean the filters according to the maintenance in the manual.

Further adjustment of the lawnmower carburetor with your own hands is done with the adjustment screws. There are three in total:

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

You have to find the maximum rpm at idling speed. To do this, slowly turn the screw (L) to the right and left.

Always turn the screw a quarter turn counterclockwise to adjust.

the lower one (T) is in charge of the engine adjustment at idle speed.

For the correct adjustment exactly the idle speed is characterized by:

  • steady operation of the cold engine;
  • not overrunning the revolutions of the hot engine;
  • for the trimmer head a large RPM margin;
  • stable engine operation when changing the position (sudden raising or lowering of the blade).

Left (H). mixture adjustment at high revs. (The screw should be adjusted last).

grass, trimmer, gasoline

The left-hand (H) screw determines the overall adjustment of maximum rpm, engine output, temperature and gasoline consumption.

Adjusting the lawnmower carburetor with the last screw is as follows:

  • Open the throttle to full, while giving full throttle. Turn the screw clockwise until the revolutions drop (in this case adjust it by ear).
  • Turn the screw as slowly as possible counterclockwise until the engine is uneven.
  • Then turn it back just a little bit, just when you hear a steady, even rpm.
  • It is more convenient to look at the work of an experienced user to apply the skills more clearly:
grass, trimmer, gasoline

It is interesting that from the point of view of the author of the video, the setting (its correctness) is determined by the color of the candle, and not only by revolutions and engine stability.

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

Adjusting a brushcutter carburetor in practice. video

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Hi! You have an excellent article, and in general the site is very curious and informative. I wish you good luck and prosperity in your business. I spent a lot of time studying automotive issues. Best of luck)))

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