DIY Stihl 250 Chainsaw Carburetor Adjustment

How to adjust the carburetor on chainsaws

To understand how to properly adjust the carburetor on a chainsaw, you need to see it, and then suggest it to the reader Pay attention to the example below.

To make the adjustment, you only need a slotted screwdriver, however, it will NOT be possible to fine-tune the carburetor without a tachometer (of course, if the person is NOT a minder or a professional driver with experience). Now let’s try to understand how to adjust the carburetor in a given situation.

Determining the need to adjust the carburetor on a chainsaw

Before you start adjusting the carburetor on a chainsaw, you need to make sure that it is generally required. It would seem an absurd phrase. However, in 90% of cases, when an inexperienced craftsman considers such an action necessary, the unstable operation of the instrument is associated with other reasons, including:

  • Problems in the fuel lines and the filter. blockages, depressurization;
  • Exhaust system malfunction;
  • Clogged or damaged air filter;
  • Unstable operation of the ignition system;
  • Violation of the tightness of the engine crankcase.

Only if these problems are excluded, and the engine is unstable, it is safe to say that carburetor adjustment is required.

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How to set up a chainsaw carburetor if it won’t start at all

Quite a common problem in cases when a “master” from the “I know everything” series tries to get into the settings with his hands, growing NOT from the shoulders. In such cases, there are standard screw positions from which you can “dance” further. First, you need to completely tighten both screws (do not overdo it). Then Unscrew:

  • Screw L. one turn;
  • Screw H. one and a half turn.

As for the idle screw, the throttle must first be completely closed (screw T removed). After that, it must be turned one and a half turns clockwise and try to start the engine. If it did not work out, it is gradually added by a quarter of a turn before starting. When the engine starts to work, the position of the idle screw is adjusted so that the GIS is not GLH, but the chain is still in place.

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How does the carburetor of a chainsaw work, on what principle does it work

Modern car engines are no longer equipped with a carburetor. Meanwhile, before, almost every driver knew how to adjust it. Today, chainsaws with injection engines have already begun to appear on sale, but the carburetor models will hold the palm for a long time, because their cost is 5-15 times lower than in the modernized version.

The carburetor consists of several main parts:

  • Aluminum body;
  • Diffuser and air damper at the inlet;
  • Nozzles (valves for adjusting the fuel supply);
  • Sprayer (it is he who provides injection)
  • Fuel (float) chamber.

The principle of operation of a chainsaw carburetor is quite simple. Fuel is supplied continuously, and its quantity is regulated by a jet. Air enters through the air damper due to the air vacuum generated by the piston. The diffuser mixes fuel and air. It is this fuel-air mixture that enters the cylinder, forcing the engine to work.

Mechanic at home: adjusting the carburetor of a chainsaw with your own hands

Any internal combustion engine requires periodic maintenance, It doesn’t matter if it is the engine of a simple moped or a powerful multi-ton tractor. Such a tool as a chainsaw was no exception. After all, it is equipped with a single-cylinder two-stroke internal combustion engine, which also requires serious maintenance, although it is much easier to perform the necessary actions here. In today’s article we will talk about how to adjust the carburetor of a chainsaw with our own hands, find out how difficult it is, and figure out whether you need to be a professional mechanic to do this kind of work.

How to correctly and accurately adjust the carburetor: Step by step instructions

In order to make the information easier to perceive, we propose to consider it on the basis of photo examples with a description of actions in tabular form. The basis is a chainsaw with Initial settings.

Read more You can get acquainted with the master class on adjusting the carburetor of a chainsaw in this.

Preparing for carburetor adjustment

Of paramount importance in setting all fuel metering characteristics of the Stihl 250 model is the uppermost adjusting screw located near the muffler. The factory setting, the parameters of which are shown on the upper plastic cover, provides that it must be unscrewed one turn from full twist.

Through the process of operation, the carburetor of the Stihl 250 chainsaw is adjusted by hand. Unscrewing the screw makes the working mixture richer, since the air-fuel mixture receives more gasoline, and tightening the screw makes the working mixture leaner, since the air-fuel mixture receives less gasoline.

Carburetor adjustment will not give positive results if there is air leakage from the engine side through:

  • Carburetor gasket;
  • Accelerating pump rubber ring;
  • Crankshaft oil seals.

Setting up the Stihl 250 carburetor is carried out only after a careful inspection, identifying existing air leaks. The next stage of the preparatory commissioning work is a complete maintenance of all units and mechanisms.

  • Cleaning from deposits, slags, resins;
  • Washing the engine with the use of a solvent, acetone;
  • Replacing the spark plug;
  • Cleaning, washing the air filter;
  • Checking the tension of the cutting chain;
  • Idling setting;
  • Warming up the engine to operating temperature.

Then you can start complex manipulation settings.

Need for adjustment

Throughout the entire operation process, it periodically arises the need for additional adjustment and ensuring the correct supply of the fuel-air mixture. How to determine exactly when and what setting needs to be done for the equipment to function normally? There are characteristic signs when the mechanism, according to the behavior of SEPARATE parts, itself tells when adjustment is necessary.

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First of all, each time before starting the engine again, it is necessary to check the color of the spark plug electrodes.

By changing it, you can make a decision on the need to adjust, adjust work processes, improve the quality of the combustible mixture:

  • Black electrodes covered with soot or carbon deposits indicate an over-enriched air-fuel mixture entering the engine.
  • Brick-gray electrodes indicate that the mixture is ideal in its composition and no additional adjustments are required.
  • White coating on the electrode of the candle indicates that the mixture is lean.

The signs outlined in paragraphs 1 and 3 indicate that carburetor adjustment is extremely necessary for the Stihl 250 chainsaw.

Precise settings will allow you to achieve maximum performance of the unit while reducing the external necessary conditions for its operation. Successful debugging of operating conditions prevents oil starvation and engine failure due to insufficient lubrication. After all, the lubricant enters the saw cylinder along with a lean air-fuel mixture.

Carburetor device

In fig. 1 shows a modern carburetor for a chainsaw made in Germany “Stihl 250. It is a unit the size of half a human fist. The manufacturer of the mechanism is Walbro, Taiwan. Case material. stainless steel alloy. A flap is fixed at the bottom of the device, which ensures a uniform supply of the fuel-air mixture to the engine combustion chamber.

Holes are also made here for attaching the assembly to the power unit body. A gasket is installed between the flanges of the mixture supply and the combustion chamber of the engine. An accelerator pump is located under the throttle stem. It is a small piston with a rubber ring.

On the front of the case there is a series of easy-to-use spring-loaded adjusting screws:

  • Idle move;
  • Maximum speed;
  • The amount of the mixture;
  • Mix quality.

The Stihl chainsaw carburetor is adjusted with These screws.

The main innovative feature of the carburetor for the Stihl 250 chainsaw is the heating device. In order to avoid freezing of the mechanism during operation during the winter period, it is equipped with a special system that preheats the steel case during operation. For this, the unit is switched to winter operation.

The body is blown with heated air sucked in from the engine. This mode of operation of the mechanism prevents icing, freezing of the jets, and ensures normal supply of the fuel-air mixture. When switching over to summer operation, the hot air flap is closed. Summer mode is characterized by natural cooling of the unit.

Do-it-yourself Stihl 250 chainsaw carburetor adjustment

For the small, compact mechanism of the Stihl 250 chainsaw, the correct carburetor setting is key. All well-coordinated work, all load modes and its trouble-free operation directly depend on the adjustment of the fuel supply systems, the quality and quantity of the fuel-air mixture. This article describes how to adjust the carburetor for the Stihl 250 and set up all of its dosing systems.

Stihl 250 chainsaw characteristics

model 360 250 440 341 361
Cylinder volume, cm³ 61.5 50.2 70,7 59 59
power, kWt 3.4 2.6 4.0 3.1 3.4
Maximum rpm No load, Tires 13500 14000 13500 13500 14000
Torque, Nm 3.7 2.7 4.50 3.6 3.7
Vibration on the tubular handle, m / s 2 3.5 3.4 4.2 3.1 2.9
Vibration on the back handle, m / s 2 5.5 4,3 4.5 3.1 3.6
Fuel tank volume, l 0.63 0.47 0.78 0.69 0.69
Oil tank volume, l 0.32 0.32 0.40 0.33 0.33
Specific weight, kg / kW 1.7 1.8 1.5 1.8 1.6
Weight without dir. Tools, kg 1.7 4.7 5.9 5.5 6.6

Stihl 250 chainsaw carburetor adjustment

Step-by-step adjustment of the Stihl MC 250 carburetor with a rev counter is carried out in the following sequence:

  • Turns off the engine, screws H and L should be tightened to the stop, then turn both of them one turn.
  • Start the engine, warm it up. At maximum speed with screw H, achieve a maximum crankshaft frequency of 14,000 rpm, recorded by a tachometer or an engine revolution counter. Hold the maximum engine speed for NOT more than 10 seconds.
  • Use the bolt LA of the idle speed stop to start the chain movement. Then screw LA back turn counterclockwise.
  • Check the acceleration of the Stihl 250 chainsaw mechanism.The carburetor adjustment continues if the idle speed is unstable or the chainsaw does not accelerate enough. Screw L must be turned back slightly counterclockwise. At the same time, the saw should quickly gain momentum, operate stably at idle speed. Make final adjustments with the LA screw. According to the tachometer, the idle speed must correspond to the catalog value of 2800 rpm.

Similarly, the carburetor of the Stihl 211 chainsaw is adjusted by hand.

In his article, the author highlighted in as much detail as possible all the details of adjusting the familiar mechanism made in Germany called the Stihl 250 saw. Adjusting the carburetor is simple and accessible to every home craftsman. Following the recommendations outlined by the author of the article, everyone can customize their Stihl 250 chainsaw and enjoy its flawless operation.

Fuel Ratio

Engine oil for STIHL 2-stroke engines 1:50:

1:50 = 1 part oil 50 parts gasoline

Other branded engine oils for two-stroke engines of vehicle classification:

1:25 = 1 part oil 25 parts gasoline

Examples of fuel mixture ratios:

If you have any questions about adjustment, see the instructions for adjusting the carburetor on the Stihl 230 and 250 chainsaw:

First stage

The adjusting screws for the highest and lowest speed should be moved clockwise until the highest resistance is encountered. When the screws reach the stop, you need to move them in the opposite direction and leave them after 1.5 turns.

Checking acceleration work

A little research needs to be done. Device acceleration is initiated. The serviceability of the engine should be assessed during the maximum revolutions. When the engine is functioning correctly, then when you press the accelerator, the speed rises quickly to 15,000 rpm.

If this does not happen or the increase in speed is too slow, it is necessary to use the screw marked with the letter L. It turns counterclockwise. Moderate movements must be observed, since the turn cannot be more than 1/8 of a full circle.

What you need to have to set up and adjust a chainsaw with your own hands

Every carburetor owner must have the right tools to adjust this system. There are three adjusting screws, which are located on the body of the device. They have their own markings:

  • L. screw for low speed correction.
  • H. screw for adjusting high speed.
  • T. regulates the idle speed, in most cases it is used for experiments.

Before adjusting the carburetor, you need to prepare the device:

  • The engine warms up, that is, it starts about 10 minutes before the repair, and turns off when you start work (see How to start a chainsaw).
  • The air filter is checked and washed.
  • The chain is stopped by turning the screw T as far as it will go (see Chain oil).
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To carry out a safe repair, you need to prepare a flat surface where you can carefully position the device, and unscrew the chain in the opposite direction. We need a tachometer. It determines the presence of a malfunction in the carburetor. When the screws are turning, the sound should be Perfect and absolutely even. If squealing notes are noticed, then the mixture is oversaturated.

About the carburetor device

The carburetor serves to mix the combustible mixture with air in compliance with predetermined proportions. If the exact dosages are NOT followed, the correct operation of the engine is jeopardized. When a large amount of air enters during the mixing of the components, and there is not enough fuel, then such a mixture is considered “poor”.

Over-saturation must not be allowed, since with a large amount of fuel in comparison with air, malfunctions or engine wear are also possible. Carburetor adjustment is necessary Not only before the initial introduction, but also when any deviations in its operation are detected. Before starting work with the chainsaw, do not forget to run it in.

The carburetor design contains a standard set of elements, but it may vary slightly depending on the manufacturer. Components:

  • The foundation. It is a special tube that visually resembles an aerodynamic structure. Air passes through it. In the transverse direction, a damper is located in the middle of the pipe. Its position can be changed. The more it is Pushed into the passage, the less air enters the engine.
  • Diffuser. This is the tapered part of the tube. With its help, the air flow rate increases exactly in the segment from which the fuel comes out.
  • Fuel supply channels. The fuel mixture is contained in the float chamber, then passes into the nozzle, from which it flows into the sprayer.
  • Float chamber. It is a separate structural element, reminiscent of the shape of a tank. Designed to constantly maintain an optimal level of fuel fluid in front of the entrance to the channel where the air comes from.

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The main stage

The engine starts at medium speed and warms up for about 10 minutes. The screw responsible for adjusting the idle speed must move clockwise. It is released only when the engine comes into stable operation. It is necessary to check that the chain does NOT move during this process.

In idle mode, the engine may stall (the reason is here). In this case, immediately turn the adjusting screw clockwise until it stops. Sometimes the chain starts to move. In this case, turn the adjusting screw in the opposite direction.

Symptoms of malfunctions and breakdowns in which carburetor adjustment is required.

The following symptoms and malfunctions indicate the need to adjust the carburetor:

  • The engine starts up with an effort and stalls almost instantly;
  • Gasoline consumption is too high, the exhaust is too thick, the combustible mixture in the cylinder does NOT completely burn out;
  • The factory settings of the chainsaw carburetor are knocked down (due to vibrations or unsuccessful attempts to adjust)
  • Malfunctions of the air cleaning system, which led to the ingress of debris particles into the mechanism for distributing the fuel mixture;
  • Significant wear of the piston group. carburetor setting in this case Acts as a temporary measure.

It is clear that if dirt gets into the fuel system with one setting, the problem cannot be solved. it needs flushing. If the piston is worn out, a major overhaul is required. However, in all THESE cases, the carburetor is also adjusted.

How to properly adjust China-made dust. adjustment instructions

In order to correctly configure the carburetor of a Chinese chainsaw, you must first remember the factory settings of the device, then turn on the engine. Subsequently, you will have to leave it to work for several hours in order to accurately set your own parameters. Sometimes work is performed once after ten minutes of engine operation, however, many Chinese-made models require special handling.

Adjustment procedure:

  • Activities start in idle mode. With the help of the adjusting screws, you need to achieve a systematic set of revolutions by the engine, therefore, you should first let it run at low speeds. The deviation from the norm is the movement of the chain along the tire. In this case, it is necessary to adjust the extreme screws to the optimal position so that the chain remains stationary.
  • The transition to average speed turns is carried out. Sometimes the engine will smoke. This defect can be eliminated by tightening the screw to supply a leaner fuel mixture.

In this case, the smoke will disappear, but the engine speed will increase. It is necessary to adjust the settings to reach the level when, when you press the throttle, the engine smoothly picks up speed, and you do not hear sudden jerks or interruptions.

  • The device motor is being checked. The chainsaw is moved to minimum speed, and then the lever is pressed rapidly. At maximum pressure, it is held for 3 seconds. If there is a malfunction of the engine, gradually loosen the screw until the optimal position is reached.
  • The chainsaw should run for several hours under real conditions. It is necessary to engage in sawing wood, and then inspect all the elements involved in this event. If there are deviations, they must be corrected using adjusting devices. When all defects have been eliminated and the optimal settings have been established for supplying correctly concentrated fuel, the process of setting up the device can be considered complete.
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    Do-it-yourself Stihl chainsaw carburetor adjustment. DIY chainsaw carburetor adjustment

    A chainsaw is a tool that will come in handy in any dacha economy even for amateurs, it does not already speak of professional workers. But, like any other device, a chainsaw needs constant care and prevention. One of the most common procedures is adjusting the carburetor of a chainsaw due to a past incorrect setting.

    Repairing the chain lubrication system

    Consider three main faults:

    • Oil leakage. Check if the pipes are tightly connected to the pump connection and if they are not cracked. Problem tubes are sealed or replaced.
    • Insufficient oil supply. Most likely clogged grease passages.
    • Cracks in the oil pump housing. Part replacement required.

    Here’s how to diagnose the lubrication system:

    Constructive components of the chainsaw

    All chainsaws are similar in structure, regardless of whether they are European (ECHO, Stihl, Husqvarna) or domestic (Kedr, Ural). The main elements are located inside the body. the fuel tank and the engine, and outside the starter, the handle, the saw part (tire) with the chain. A sharp jerk of the cable starts the engine, and that one. the saw blade.

    To begin with, we suggest that you familiarize yourself with thes that show how the chainsaw works and how it works:

    From time to time, the saw malfunctions, which require disassembly to eliminate. What can happen to such a simple mechanism as a chainsaw? At least the following:

    DIY Stihl 250 Chainsaw Carburetor Adjustment
    • Stops starting;
    • Starts up, but soon stops;
    • Ceases to function in the cut;
    • Loses its power;
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    Most of the malfunctions are associated either with interruptions in the operation of the engine (fuel supply system, exhaust system, ignition, cylinder-piston part), or with malfunctions of second systems and assemblies (clutch, chain brake, tire, lubrication system). Consider the most common breakdowns and techniques for their elimination.

    A serviceable chainsaw starts with one jerk and does not fail in the cut

    Do-it-yourself chainsaw repair: analysis of major breakdowns and methods of their elimination

    It would seem, why would a summer resident need a chainsaw, who is engaged in growing vegetables and fruits, or to the owner of a country house with a small garden and several flower beds? The question disappears when there is a desire to build a bathhouse, update a greenhouse, knock down an old business, or just make a bench for relaxation. Unfortunately, any mechanism periodically needs prophylaxis and replacement of spare parts, and for this you need to be well versed in the device of the product, in addition, repairing a chainsaw with your own hands will save time and money.

    Fuel supply system repair

    Fuel may not enter the cylinder for the following reasons:

    • Dirty fuel filter. Remove the fuel hose and check how the fuel flows. If the jet is weak, the filter may need to be cleaned. It is taken out of the fuel tank filler hole and cleaned; in case of severe contamination, replace with a new one. As a preventive measure, it is recommended to replace the fuel filter every three months.
    • Clogged breather (holes in the fuel tank cap). Check also by disconnecting the hose, in case of blockage, clean with a needle.
    • Lack or insufficient fuel. There may be several reasons for the malfunction. The first reason is a clogged air filter. Air ceases to flow into the carburetor in the right amount, in this regard, due to a too rich fuel mixture, the engine’s operation is disrupted. The contaminated filter is carefully removed, cleaned and rinsed in water, then dried and reinstalled.

    Another reason is improper adjustment of the carburetor. Adjustment is made with three screws.

    Timely replacement of the fuel filter ensures full fuel supply

    Fuel hose and choke actuator Must fit snugly against the fitting

    The throttle cable must be in place

    During work, you must use the instructions, otherwise you can only make it worse.

    And the last reason is a violation of the integrity of the membrane or clogging of the carburetor channels.

    To repair the carburetor yourself, you need to get acquainted with all its parts.

    All parts must be clean, dry and in good condition.

    Dismantling and cleaning the muffler

    If the engine works fine at low speeds, and at high speeds it starts to stall, the reason may lie in the muffler spark arresters, clogged with combustion products.

    • Remove the muffler;
    • Disassemble (there are also non-separable models);
    • Cleanse from carbon deposits using detergents;
    • Dry with a hair dryer;
    • Reinstall.

    Dry cleaning is unacceptable, as the soot contains carcinogens, the inhalation of which is hazardous to health. After removing the muffler, the outlet is closed with a clean cloth.

    Interruptions in the operation of the chainsaw signal a possible clogging of the muffler

    To prevent clogging of the muffler, it is necessary to monitor the composition of the fuel mixture. The amount of oil should not exceed the rates recommended by the manufacturer. Poor oil quality also negatively affects engine performance.

    Assessment of the state of the cylinder-piston group

    Often the engine will not start or run at full capacity due to low cylinder pressure. It can be caused by piston or cylinder wear, piston ring sinking, bearing wear. You can partially examine the state of the cylinder-piston group (CPG) by removing the muffler and looking into the opened hole.

    A compressor placed in the plug hole will help to measure the compression in the engine. according to the measurement results, you can also talk about the state of the CPG. Accurate data is obtained only after the complete disassembly of the mechanism. If the piston is chipped or scratched, it must be replaced. The piston ring must be clean, free of carbon deposits, and exactly in its place.

    Piston and crank mechanism wear is considered a serious problem.

    According to the results of measuring the compression, one can judge the condition of the parts of the CPG

    Checking the ignition system

    The first thing to do in the event of a chainsaw breakdown is to inspect the spark plug by disconnecting the wire and carefully unscrewing it with a special key.

    The components of the chainsaw ignition system: 1. flywheel with magnets, 2. ignition module, 3. spark plug, 4. high voltage wire

    Unscrew the spark plug to check its condition.

    Her appearance says a lot:

    • Dry. Most likely, the fuel mixture does NOT enter the cylinder. It’s not about the ignition system, so the plug is screwed back.
    • Strongly splashed with fuel. The reason for the excess fuel mixture lies either in the violation of the starting rules, or in the improper adjustment of the carburetor. The spark plug is carefully wiped, shut off the fuel supply and turn on the starter. to remove excess fuel and ventilate the combustion chamber. Then the candle is placed in place and the mechanism is started again.
    • Covered with black carbon. This may indicate the use of low-quality oil, in an incorrectly adjusted carburetor or in an incorrectly calculated ratio of gasoline and oil. The candle should be washed, cleaned of carbon deposits with a sharp object (awl or needle), wipe the electrodes with a sandpaper and put in place.

    When checking the candle, you must Pay attention to the gap between the electrodes: it is considered normal from 0.5 to 0.65 mm. A damaged or worn gasket must be replaced.

    A large amount of black carbon on the spark plug indicates an engine malfunction.

    To be sure, you should also check for a spark. To do this, put the ignition cable on the spark plug, pliers connect the plug nut and the cylinder, start the starter and watch for the spark. If it is missing, the plug must be replaced. If the new spark plug also does not emit sparks. the problem is in the high-voltage conduction or in the broken connection with the spark plug.

    Adjusting the chain brake

    The chain brake is often triggered due to grease or sawdust clogging the brake band and the space under the cover. All parts should be cleaned from blockages. Perhaps the tape is simply worn out, then it needs to be replaced.

    The chain brake is restored by mechanical cleaning

    Some parts of a chainsaw will wear out faster than others. These include the drive sprocket, bar, chain, anti-vibration elements. For quick replacement, it is best to always have spare parts on hand. Chain sharpening should NOT be neglected.