How to Properly Adjust a Chinese Chainsaw Carburetor

Owners reviews

Nikolay Astakhov, 44, of Primorsky Krai:

I bought the Poulan 2150 four years ago. I use it regularly, mainly for cutting and chopping firewood. I still have an American assembly, if you can believe the paperwork. No special problems during this time was not detected. The motor works fine, the bar and chain are included in an acceptable quality. Since then I adjusted the carburetor a couple of times and bought a couple of chains.

Victor Rybak, 43 years old, Arkhangelsk region:

I bought the Poulan saw as an American-made one, but it turned out to be made in China. However, in quality of parts and assembly of the unit is quite acceptable. The engine is almost unbreakable. I’ve put a lot of weight on it. it saws just fine. Of course, during this time was not without problems. The main one is the carburetor. It has to be adjusted regularly. The Poulan 2150 chain saw is very susceptible to air filter debris: the slightest thing gets muddy and the rpm is already floating.

The advantages of the Poulan model: price, quality engine, no vibration;

Disadvantages: often knocked down settings of the carburetor, Poulan strongly responds to contamination of the air filter.

How to properly adjust the carburetor with his hands?

After flushing and cleaning the carburetor, reassemble it and adjust it. First of all, it is necessary to understand the purpose of the adjusting screws. The manual will help with this, but some general points should be considered at once. The most common is the following designation of screws:

  • H. adjusts the state of the main jet, t.е. L. adjusts the maximum speed of the engine shaft rotation;
  • L. adjusts the no-load jets (responsible for the minimum speed of rotation of the shaft);
  • T. adjusts the idle speed of the motor. may also be designated by the letters LA or S, on some models of carburettors it is absent at all.

Turning the screws H and L clockwise depletes the fuel-air mixture and counterclockwise enriches it (the amount of gasoline increases). Turning of screw T changes idling speed of the shaft. clockwise. it increases, and in the opposite direction. it decreases.

Figure 2. Carburetor adjustment mechanisms

Before proceeding to direct actions, it is necessary to find and carefully study information on position of adjusting screws (values of rotation angles during adjustment). This information is available in the instruction manual of the chainsaw. Then get your saw ready for work by placing it on a flat, level surface with the chain facing away from you. Disconnect all covers, remove the foam and air filter. At this point the preparatory operations are considered to be completed, you can start the main part of the work.

  • Slowly turn the screws H and L clockwise as far as they will go. Be careful not to break the screws: doing so will cause complete loss of the carburetor.
  • Slacken both screws by 1.5 turns.
  • Run the engine for 10 minutes and warm it up. This is a necessary moment, because the carburetor can’t be adjusted correctly on a cold engine.
  • Turning the screws H and L, alternately adjust the rotation of the shaft at maximum and minimum revolutions.
  • By adjusting the position of the T screw (or it may have another designation) the idle speed of the chainsaw is adjusted. Try to get the engine to run smoothly and steadily. It is important to watch whether the chain moves at idle speed or not. If it moves, turn the screw a little more counterclockwise.
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Important! Screw H should not be adjusted by an inexperienced person. If it will be set incorrectly, at maximum speed in the combustion chamber of the cylinder will be fed leaner air-fuel mixture. This will lead to an accelerated wear of the piston group.

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You can check the engine operation visually and by ear. If the mixture is too enriched, there is thick smoke from the exhaust port. A whistling noise is heard when the saw is running with a lean mixture. Overly economical mode is harmful. if you set the propeller L to “lean” fuel, you will have problems starting the engine. Setting the propeller screw H to leaner fuel would significantly reduce the power output. The following signs are an indication of the correct setting:

  • The engine does not idle and the chain does not move;
  • there is no excessive smoke from the exhaust pipe when the engine is running;
  • the engine has good good good response (goes up quickly when you press the gas pedal).

Setting Fuel Mixture to Factory Settings, Chainsaw

A detailed description of the adjustment is available in the instruction manual that comes with the tool in the delivery set. It should be studied carefully, because there may be some peculiarities or specific requirements set by the manufacturer and related only to this saw model. If all the requirements are followed exactly, the chainsaw’s performance will be restored to its original state.

Chainsaw carburetor repairing Part.1

How a chainsaw carburetor works. principle of operation

Operation of this unit, despite its complex design, is simple and understandable even for beginners. The principle of operation is based on the following steps:

Carb Adjustment on The Chinese Chainsaw

  • As soon as the engine of an internal combustion engine is started, the air damper is opened
  • In the area of the narrowing of the diffuser 16 the incoming air flow is accelerated, which is mixed with the gasoline-oil mixture
  • The petrol-oil mixture is fed through nozzles no. 15 and 12, and the air passes through the filter placed in front of the inlet, before going through the butterfly valve 7
  • The air damper 8 is located behind the diffuser, and serves to regulate the amount of mixture in the combustion chamber
  • With the screws 17 and 10 the volume of gasoline that passes through the jets is adjusted. On the carburettor control panel, these screws are marked L and H
  • The needle valve 11 is used to regulate the volume of the fuel mixture in the float chamber 14. To adjust the needle valve, a diaphragm 13 is installed in the mechanism
  • Another diaphragm 4 is responsible for the fuel supply to the combustion chamber of the cylinder. The position of this diaphragm depends on the number of revolutions of the internal combustion engine
  • A fine filter is used to clean the oil-petrol mixture

The simple principle of operation of the carburettor ensures smooth operation of the engine. The quality of the adjustment affects how the machine behaves when idling and during operation. The mechanism in question has a direct effect on the performance of the entire tool. The quality of the adjustment determines the service life of the tool.

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The most optimal carburetor designs for chainsaws have been developed by the world’s leading manufacturers. German STIHL, Japanese Walbro and others. These best designs are hard to beat. Therefore, most Chinese manufacturers copy the best models.

Today there is a large supply of Chinese carburetors for chainsaws on sale.

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Some are nameless, from an unknown manufacturer and do not even have a label. They are offered simply for a particular chainsaw model. For example, a carburetor for the STIHL MS 361 chain saw.

Others have brand names of famous brands.

Others have their own catchy names. in Russian transcription King-cong, Technopark, Reset and others.

The design and principle of operation of a chainsaw carburetor

A chainsaw carburetor consists of the following main assemblies:

  • All-metal body, made of lightweight aluminum alloy;
  • The carburetor has a diffuser located at the carburetor inlet;
  • jigglers, special valves designed to regulate the flow of the combustible mixture;
  • atomizer;
  • float chamber.

Below is a diagram of a Walbro carburetor, which is often installed on chain saws. Using this diagram, it is possible to study in more detail the internal structure of the chainsaw carburetor.

The carburetor may have 2 or 3 adjusting screws with springs. The adjusting screws are designed so that there are needles (cones) on their ends. The screws have a right-hand thread, i.e. they are tightened clockwise.

The chainsaw carburetor works as follows.

  • After starting the combustion engine the air damper opens.
  • In the diffuser (16), where there is a constriction, the air flow is accelerated and mixes with the petrol. The latter comes in through the nozzles (15) and (12), and the air cleaned by the air filter comes in through the slide valve (7), located at the diffuser inlet.
  • The restrictor flap (8) located behind the nozzle controls the amount of precured mixture that enters the combustion chamber.
  • The volume of the petrol passing through the nozzles is regulated by the screws (17) and (10), which are the L and H respectively on the chain saw.
  • The needle valve (11) controls the volume of fuel mixture in the float chamber (14). The needle valve is controlled by a diaphragm (13).
  • The diaphragm (4) controls the fuel mixture in the combustion chamber and this depends on the engine speed. Gasoline is cleaned through the filter (6).

Does it need to be disassembled?

It is possible to regulate a chainsaw carburetor without any disassembly at all, in rare exceptions it is necessary to remove the air filter cover. This is not without controversy: The chainsaw is designed for easy access to the adjustment mechanism on the one hand and it is recommended that you do not have to use it as often as possible on the other hand.

It’s true that experienced woodcutters and sawyers always carry a flathead screwdriver with a long sting and periodically adjust the carburetor. The reason for this is simple: when a chainsaw is made, its carburetor is roughly adjusted for a certain composition of air and fuel. It is clear that conditions on the job site are not the same as on the bench.

If you change the brand of gasoline or, for example, the humidity increases, an experienced chainsaw user will always adjust the mixture quality for better performance and less wear and tear on the piston part. But this, we repeat, requires a lot of experience with a particular chainsaw and knowledge of the peculiarities of its behavior. In addition, the adjustment is incredibly fine The screws are tightened only 1/10th of the way. 1/20th of a turn.

Another reason to adjust is to repair or replace the carburetor. In any case, the quality of the mixture should be adjusted only if the serviceability of the carburetor is reliably known (no debris, gaskets do not blow), the air filter is clean, the spark plug, clutch and ignition system are in perfect order. Otherwise, there is a high probability that the malfunction will be eliminated in a moment and the adjustment will abruptly become incorrect, and the engine will begin to run to wear and tear.

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First signs of carburetor malfunction

The chainsaw can have difficulty working from time to time because of untimely or unprofessional periodic maintenance or heavy use. For professional workers, such breakdowns can reduce their work efficiency and ruin their mood for the day.

Malfunctions of the carburetor, in turn, have specific signs. You can tell at a glance the cause of the malfunction.

The following signs are indicative of improper carburetor adjustment:

  • The tool starts up uncomfortably and then immediately stops.
  • Your chain saw stops when you step on the gas.
  • gasoline is being consumed, but there is still gas in the cylinders and the exhaust is too thick.
  • The carburetor is misadjusted due to improper carburetor adjustment or use.
  • Debris in the air intake system. This causes it to fail.
  • The engine pistons are exhausted. Tuning the carburetor in this case will only temporarily solve the problem.

If you get dirt in the carburetor, you can’t just adjust it. You just need to clean it. When the pistons are used up, you need to do an engine overhaul.

But after that, of course, it is necessary to adjust the carburetor jets, as well as their blowing and cleaning.

The structure of the carburetor

In this short review, we can not describe in detail all the details of the carburetor and thoroughly familiar with all the nuances of its work, but dwell only on the main points.

The carburetor consists of these components:

  • Tube with the air damper. A small wind tunnel, which is designed to regulate the air flow. The transverse flap, depending on its position, reduces or increases the amount of air, thinning or enriching the fuel mixture;
  • Diffuser. designed in the form of a constriction at the end of an aerodynamic tube. The main task is to increase the pressure and velocity of the air as it mixes with the fuel;
  • Nozzle, or atomizer. Designed to supply fuel and mix it with oxygen.
  • Float chamber. A special reservoir that ensures a stable level of gasoline, at the inlet to the air duct.

Poor and rich mixture

about lean and rich mixtures.

rich mixture

A rich mixture is a fuel mixture in which the amount of fuel fed to the carburetor is greater than. In this case, the fuel does not have time to burn completely and less energy is produced than with an optimal fuel/air ratio. Part of the unused fuel ends up in the muffler, then the chainsaw smokes a lot.

Poor mixture

A lean mixture has too much air, and this is not good because it has its disadvantages. Namely: insufficient flash energy (and thus a loss of power in the end), excessive heating of the cylinder due to insufficient lubrication and high rpm, which leads to galling, and there is not far to the jamming of the engine.

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