Oleo-Mac Chainsaw Carb Adjustment

The stability and reliability of the Oleo-Mac chainsaw engine (Oleo-Mac) depends on the quality of the preparation of the air-gas mixture in the carburetor, it performs important functions. it allows you to smoothly change the engine speed, control idle speed. With prolonged use, it may be necessary to reconfigure it. how to do it correctly and avoid mistakes?

What carburetors are used

Gasoline saws are installed on Oleo Mac chainsaws. Walbro diaphragm carburetors for two stroke engines. They are distinguished by simplicity of design, maintainability, unpretentiousness in operation. Walbro is part of the Stihl group of companies, and therefore produces products that meet international quality standards.

Oleo-Mac Chainsaw Carb Adjustment

Carb adjustment

When buying a chainsaw, the carburetor has factory settings and is adjusted to the optimal operating conditions. However, during operation, the engine (ICE), fuel pump, carburetor wear out, as a result of which their repair, maintenance and adjustment are required. In this case, the role of the carburetor is to limit the minimum and maximum engine speeds.

The main criteria to determine the need for adjusting the carburetor:

  • the engine does not start, stalls, does not respond to pressing the accelerator;
  • lack of idling;
  • increased fuel consumption, ICE does not develop power;
  • wear of the piston group, soot on spark plugs, black exhaust gases, incomplete combustion of gasoline.

The reasons for the carb settings failure are as follows:

  • violation of the fixing screws that regulate the minimum and maximum engine speeds due to strong vibrations or mechanical stress;
  • when the engine piston system is worn;
  • clogged air or fuel filters, jets, fuel channel, intake valve failure.

To adjust the carburetor, it is important to understand what parts and assemblies it consists of and the principle of its operation. This will determine the causes of the failure, what tools to prepare for adjustment and the type of repair kit, if repairs are needed.

Design and principle of operation

The principle of operation of the carburetor is based on mixing the fuel mixture of fuel and oil with air in a certain proportion for effective ignition and their complete combustion in the internal combustion engine. It is a one-piece housing, inside of which the following structural elements are located:

  • fuel chamber;
  • air and fuel channels;
  • jets: idle and main;
  • fuel filter mesh
  • inlet and outlet fuel valves;
  • air and throttle valves;
  • diffuser;
  • fuel and control membranes;
  • adjusting screws;
  • sealing gaskets.

Outside the housing, screws are removed to adjust the quality and composition of the mixture. In the upper and end parts there is a pipe for supplying fuel and a pulse channel of the fuel pump.

The carburetor works according to the following algorithm:

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  1. When the engine starts, the air damper opens. Air passes through the filter and bypassing the dampers (in diagram number 1), enters the inside of the housing.
  2. The fuel pump pumps gasoline into the chamber. Under pressure, the oil-gas mixture is sprayed through the nozzles (in the diagram above, position 2 is the main nozzle, 3.4 is the idle nozzles), contacts the air, mixes, and then enters the combustion chamber. The engine starts to idle.
  3. When you press the accelerator, the second adjustable throttle opens at a certain angle (this is the second damper in the photo), fuel starts to be supplied through the main jet (position 2 in the diagram). Inside the carburetor, more combustible mixture is mixed, which, when fed into the combustion chamber, increases the engine speed.
  4. The amount of gasoline entering the chamber also depends on the settings of the adjusting screws controlling the needle valves (in the diagram, these are spring-loaded screws on the left and right).
  5. The fuel supply to the chamber is limited by membranes, the feed rate is determined by the change in pressure in the piston and is controlled through the feedback of the pump and the pulse valve. The operation of the fuel pump is synchronous with the engine: the higher the speed, the stronger the flow of the fuel-air mixture.
  6. To prevent fuel overflow, a special lever and a shut-off valve are provided in the chamber.

Carburetor fuel supply system. 1. regulatory camera; 2. membrane; 3. locking needle.

Customization tools

Since the adjustment is performed using external screws, you will need a Phillips or flat-head screwdriver included in the saw set, the width of the working part is 4 mm. To control the speed you will need a tachometer.

Video: Oleo-Mac Chainsaw Carb Adjustment


Incremental adjustment

An example of carburetor adjustment is described using the Oleo Mac 937 chainsaw as an example. The principle of setting other saws is practically the same, therefore this algorithm is applicable for the following models: 941s, 936. There are no similarities with other, less popular models (for example, Oleo Mac 362 or Oleo Mac 35) checked, but most likely there are no serious differences.

Before setting up the Oleo Mac chainsaw carburetor, a number of conditions must be met:

  • clean the air and fuel filters;
  • check the condition of the nozzles, make sure their serviceability and cleanliness;
  • evaluate the integrity of the membranes: absence of damage, cracks;
  • Check that there is enough fuel in the chamber.

For standard carburetor adjustment, disassembly is not required. Outside there are screws that allow you to perform all the necessary settings:

  • L. low speed;
  • H. high speed;
  • S. idling.

Despite the fact that the manufacturer recommends adjusting only the “S” screw, in practice this is not enough. Before adjustment, all three screws should be tightened and then unscrewed by 1.5-2 turns.

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Step-by-step adjustment is performed as follows:

  1. The engine starts, warms up for 3-5 minutes at medium speed.
  2. The tachometer is connected.
  3. Adjustable operation at low speeds using the screw "L". It is necessary to achieve 1-1.5 thousand rpm. engine without scrolling the chain, and when you click on the accelerator. the absence of a failure of speed. If a failure is detected, the screw should be unscrewed until this effect is completely eliminated.
  4. High engine speeds are adjusted with the “H” screw. When you press the accelerator to the maximum, they monitor the increase in speed, it is important that they do not exceed the maximum allowable value. It is recommended to set 5-10% lower than the maximum speed so as not to provoke increased wear on the engine.
  5. The carburettor is finely tuned with the “S” screw. When the chain is idling, the screw should be turned counterclockwise until it stops. If the internal combustion engine stalls, then the screw is unscrewed clockwise until stable operation is obtained.
  6. After the tuning procedures, the chainsaw is tested in real working conditions. If necessary, carry out the setting again.

Carb adjustment video

For clarity, the setting of the carburetor of the chainsaw can be seen in the video below. After viewing it, no setup questions should arise even for beginners.

Adjustment nuances

When setting up Oleo Mac chainsaw carburetors, the following nuances usually arise:

  1. Mismatch of screw labels. Depending on the model, equipment supplier, or other factors, the labeling may differ from that described. In such cases, it is recommended that you carefully read the instructions that came with the device.
  2. After adjustment, the chainsaw needs to be turned off and allowed to cool for 10-15 minutes to check its operation from a "cold" start.
  3. In the absence of experience or the necessary knowledge to adjust the screw "N" is not recommended. This is due to the likelihood of setting up a poor-quality fuel-air mixture, which can cause wear of the piston group, failures in the start and operation of the engine.
  4. At all stages, control of the engine speed with a tachometer is required. Replacing the tachometer can be an oscilloscope or a multimeter with this function.

Carburetor repair chainsaws Oleo Mac

If Oleo Mac fails to set up the carburetor of the chainsaw, then it probably needs repair. You can determine this by the following symptoms:

  • the engine spontaneously and abruptly changes speed, stalls, does not start;
  • increased gas mileage;
  • the presence of vibrations or increased noise during operation;
  • dark exhaust fumes.

To access the carburetor, you will need to remove the cover on the chainsaw body, and then the air filter. Actions must be performed carefully and without undue effort.

Faults and solutions

Common malfunctions may include:

  • clogged filters or jets eliminated by cleaning;
  • membrane damage (acts as a pump), is solved by replacement;
  • failure of the sealing gaskets; replacement with new ones after disassembling the body parts of the carburetor is necessary;
  • jamming of the valve (a needle that blocks the fuel supply in the carburetor), an assessment of its condition is required to determine the possibility of its further operation or replacement;
  • violation of the contact of the choke lever with the accelerator; restoration, repair or replacement of the assembly is required.

Often some of these problems occur after prolonged downtime of the chainsaw. To restore working capacity, it is required to perform full maintenance of the nodes and pre-launch work.

Is it worth it to do an independent repair

Self-repair of the carburetor of the Oleo Mac chainsaw is advisable in the following cases:

  • the breakdown is simple, obvious, the necessary parts are available;
  • have experience in performing such work, qualifications;
  • the manufacturer’s warranty is not lost;
  • there is no way to contact a service center or is it financially disadvantageous.

It should be clearly understood that self-repair can not guarantee a positive outcome. Therefore, it is worth taking it only if you have knowledge of the design and principle of operation of the carburetor.

Car repair kit

To repair the carburetor, you need a repair kit, the composition of which is as follows:

  • rubberized seals;
  • diaphragms: for pump and control;
  • needle valve assembly.

Advantages and disadvantages

The main advantages of Oleo Mac chainsaw carburetors:

  • large resource;
  • compact sizes;
  • three adjustment screws for fine tuning (a feature of all modern chainsaws with membrane carburetors);
  • compact size and relatively small weight of the structure, in comparison with analogues;
  • affordable cost of parts, carburetor assembly;
  • unpretentiousness to the quality of gasoline.

It is also worth noting a number of disadvantages:

  • it can be difficult to find a repair kit for sale in small towns;
  • difficulties with the settings, high requirements for the qualifications of the adjusters;
  • the need for periodic adjustments during long-term operation.

Adjustment of carburetors on chainsaws Oleo Mac 941s, 936

There are no differences in the adjustment. The carburetor models of Oleo Mac 937, 941s and 936 chainsaws are the same. We examined step-by-step adjustment in detail, using the example of the 937 model, therefore any of the listed saws is regulated with the same approach.

Adjustment of carburetors on Oleo Mac 362 and 35 chainsaws

These models are very old and today there is practically no information on their adjustment. But, because If modern carburettors of the membrane type are used there, the principle of adjustment should be identical to that discussed in this article.

The Oleo Mac chainsaw carburetor is set up without disassembly using the adjusting screws. It is important to follow the sequence of actions, monitor changes in engine operation, strictly follow safety rules during operation and the result will be positive.