Where is the fuel filter in a chainsaw?

Chainsaw: questions and answers. Part 3.

I periodically monitor the search engine queries, which bring visitors to the site from search engines. On these requests, as well as the questions that are asked in the Комментарии и мнения владельцев I choose the most common and answer them in the section Chainsaw: Questions and Answers. Read the previous articles here: Questions and answers on the Husqvarna 137e chain saw.

So the most popular queries of the last few months:

Question: How much compression should a chainsaw engine have??

Answer: Normal compression for chainsaws is 8-12 atm (0.8-1.2 MPa). If compression is below 8 atmospheres the engine will not develop the necessary power, the torque will not be enough for stable chainsaw operation. How to measure compression in chainsaw engines? For this you need a compressometer device for measuring compression. Measurements are done on a hot engine. Sometimes for diagnostics perform measurements on the cold, so that the difference in the results to determine the cause of the problem.

Step by step: Removing the chainsaw cover. Unscrew the spark plug. It is highly advisable to dismantle the carburetor or remove the air filter. After that, the tip of the compressometer is inserted into the spark plug hole gasoline and starter cord rotate the piston to the maximum readings of the compressometer.

The most common cause of compression loss is ring wear. To check it is very simple. after you found out that at your chainsaw compression index is below normal pour into a cylinder of 10-20 milliliters of oil and check compression again. If it is too high, it is ring wear.

Watch this video on how to measure compression in chainsaws:

fuel, filter, chainsaw

Question: What is a breather valve?? Where it is in a chainsaw?

The breather valve, whose purpose is to normalize pressure in the gasoline tank as fuel is expended. Why you need to normalize compression? Since gasoline is produced, and the lid of the gas tank is sealed, a vacuum is formed in the tank, which means that the pressure on its walls significantly increases. The breather valve equalizes the pressure in the tank with the atmospheric pressure. It is located in the gas tank itself. A clogged carburetor can make a chain saw difficult or impossible to start. It’s easy to clean with a needle.

How to spot a carburetor malfunction?

Typical carburetor malfunctions are easy to recognize. This is manifested in the fact that the chainsaw engine starts and then shuts down or does not show any signs of life at all. Or consumes fuel at full speed, producing clouds of black smoke and aggressive vibrations instead of the proper power.

Diagram of a chainsaw carburetor

The carburetor settings can be disturbed in the case of a carburetor malfunction:

    The regulating screws do not lock;

Chainsaw air filter with a capron insert

Any problems detected must be corrected immediately. But how do you know if it’s the carburetor?? To do this, take a look at how your tool works.

A list of typical signs that the carburetor settings have gone off include:

This is usually caused by the use of an incorrect (lean) fuel mixture.

Expressed in increased exhaust emissions, which take on a black color. It means that the fuel is not completely consumed, t.е. the mixture is oversaturated.

Carburetor is set correctly and starts the saw on the first try

May be due to damage to the adjustment screws or the protective cap.

Indicates critical wear of the piston group, so adjusting the carburetor will delay overhaul only for a while.

Such a picture can be seen when the carburetor channels are clogged or its filters are faulty. In this case, you have to perform the adjustment only after a thorough cleaning of the unit.

Despite the fact that the carburetor is the most complex part of the engine, if you find malfunctions in its operation, you should not get upset. Instead, you need to arm yourself with some tools, a structural diagram of the assembly and sound logic.

The main purpose of a carburetor in any internal combustion engine is to mix fuel with air in certain proportions. If they are broken, the engine begins to work incorrectly or stops completely.

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The carburetors of different brands of chainsaws have some differences in design, but the main nodes of this part, as well as the principle of their operation are approximately the same:

  • The base (body) is an aerodynamic tube with an air damper that is positioned crosswise. Its purpose is to regulate the air flow into the inner chamber.
  • Float chamber. a container that holds the fuel mixture in a stable state.
  • Atomizer. the area where air and fuel come into contact. Fuel flows into the atomizer from the float chamber through the nozzle.
  • Diffuser is a part that increases the velocity of air flow and maintains the desired pressure. Diffuser is located in a narrowed part of the tube.

The principle of operation of the carburetor is as follows:

fuel, filter, chainsaw
  • After starting the engine, the choke opens and air enters the.
  • Flow rate and float level in the chamber are controlled by the position of the flap, due to the pressure difference in the float chamber and the air duct.
  • Fuel is sucked from the float chamber into the nozzle and then into the nozzle. Air is sucked in by the passing air and absorbs the fuel.
  • The resulting mixture is forced into the cylinder cavities through the intake ports.

How to Wash a Gasoline Filter on a Saw

Classic gasoline chainsaw requires periodic maintenance with replacement or cleaning of air and fuel filters.

This article will talk about how to properly perform the procedures of flushing or replacing the filter elements, as well as how often to do it.

All replacements and flushes are done only when the engine is stopped and has cooled down. Also, the spark plug must be disconnected before work is done, so that there is no unexpected starting.

If the fuel mixture does not cause complaints, then you should proceed to check the starter. If there are no complaints here either, check the condition of the spark plug. The device should be unscrewed and check the width of the gap, which for the ideal operation of the chainsaw engine should be 0.5 mm. Notice if the spark plug is dry or wet. If dry. look for a problem in the carburetor, which most likely turned out to be clogged and does not supply the fuel mixture into the combustion chamber. Remove the carburetor, carefully wash and clean it. If the carburetor delivers fuel but the chainsaw will not start, look for the problem in the cylinder and piston assembly. Dismantle the cylinder and look inside, looking for possible cracks and chips. If they are found, the cylinder should be replaced or given to repair for boring. After that, pay attention to the condition of the piston o-rings and their grooves. They have to be in a condition that allows the piston to be kept in the sleeve so the compression level is sufficient.

Clean it properly

To qualitatively clean the chainsaw, you will need the following tools:

  • Phillips screwdriver and flathead screwdriver,
  • wrenches with sockets of different sizes,
  • a special cleaning compound, a cloth for cleaning,
  • ultrasonic cleaner.

You can see the set of tools on the photo.

Cleaning the carburetor of a chainsaw should be performed according to the following algorithm:

  • To begin with it is necessary to drain the remaining fuel from the fuel tank. Remove the chainsaw cover by unscrewing the fasteners. Take out the filter and disassemble the body, removing the nuts and locks if necessary.
  • Remove the fuel mixture hose from its retainer, unscrew the fasteners of the upper cover of the carburetor. Then remove the top cover and the blue gasket. this is the fuel pump membrane. On the left side of the body there are spring brackets, remove them, and then the screws. It is desirable to sign the parts and fix schematically the places from which they were removed, so that nothing is mixed up at the time of assembly.
  • Remove the carburetor bottom cover, unscrew the screw and remove the needle valve and the spring under it. Then use longitudinal force to remove the choke and throttle axle.
  • Let’s remove the throttle flap, throttle actuating lever and throttle axle.
  • Lay all removed carburetor parts on a level surface and examine them for integrity. Parts with a high degree of wear should be replaced with new ones.
  • Wash the parts with a specialized cleaning agent and dry them with a lint-free cloth. The tubes should be pressurized with a pump.
  • For maximum cleaning effect, the carburettor on your STIHL chain saw can be cleaned in a special carburettor bath that produces a cavitation effect. The bath is filled with diesel fuel, and carburetor parts are immersed in it for several minutes. At the end, dry the parts with a pump.
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A detailed video of the cleaning process will help you to do the job properly.

After all items are dried, it is necessary to assemble the carburetor. Detergent normally evaporates completely in 24 hours. It is better to wait 24 hours after cleaning, because detergent residues on the parts can get into the fuel tank and emit toxic gases when burned.

Another important nuance related to the disassembly of the chainsaw is that it is necessary to install and adjust the needle valve paddle extremely accurately, otherwise the chainsaw may not start. To check the correct positioning of the petal, you can use a blade. After placing it on top, check how freely the paddle rotates. If there are no problems, everything is fine. you can continue with the assembly. If you do encounter running problems, the blade must either be pressed down or the edge of the blade must be bent.

How to remove the carburetor from a chainsaw?

Or the engine does not start or immediately stops, most likely the carburetor is clogged and needs cleaning. How to check the carburetor chainsaw? You’ll have to disassemble it. there’s no other way.

Before cleaning the carburetor on the chainsaw, it is still recommended to check the other assemblies: air and fuel filters, spark plug and muffler. It is possible that they are clogged. it is easier to clean the filter or replace the spark plug than to clean the carburetor on a chainsaw. By the way, it is a problem with the candles is the reason why the chainsaw shoots into the carburetor. too late ignition leads to the fact that an excess of fuel-air mixture is formed, as it does not have time to burn completely.

In case the problem is not corrected, you will have to remove the carburetor. It is very easy to do:

  • Remove the plastic back cover. it is held on the retainer or on the thread.
  • Dismantling the air filter.
  • With a flat screwdriver you need to pick up the air rods and remove them. There may be two or three rods, depending on the model.
  • The carburetor is fastened with two fasteners. they are located diagonally. It is necessary to unscrew them.
  • Disconnect the gasoline hose that carries fuel to the carburetor from the gasoline tank.

The design and operation of the individual units

The chainsaw is designed to be operated by mixing fuel with oil. This solution is then poured into the gas tank, from where it is delivered to the engine and ignited with a spark. Next, the motor and the chain path function independently, and to set the cutting side in motion, it is necessary to press the throttle button.

Before each process, it is important to inspect the available elements of the chainsaw design for serviceability: the chain should be well tensioned, the moving mechanisms lubricated, the air filter was in good condition. It is recommended that you clean all dirt and shavings from the tool after you have finished cutting.

The ignition system

The design of modern gasoline-powered saws has a non-contact electric starting aid. Thanks to this structure, the user no longer has to worry about adjusting the air gap and cleaning the contacts. This includes the following parts:

Shaft turns create electrical signals that are transmitted to the candle through the circuitry. The fluid is ignited as a result.

fuel, filter, chainsaw

The carburetor unit

The task of this device is to mix the fuel mixture with oxygen. The air flow to the carburetor is controlled by a wind tunnel with a flap. There is also a float inside the unit that adjusts the position of the flap. When the chainsaw engine is turned on, the valve opens, oxygen enters the diffuser, mixes with the fuel and moves into the cylinder cavities.

The gas knob adjusts the width of the open flap, resulting in increased air flow and higher piston speed.

Clutch mechanism

The modern saw has a centrifugal clutch that engages automatically when the throttle key is pressed. The shaft is pulled by springs which relax according to the increasing rate of rotation. Then the drum rotates and the saw chain starts to come into action. There is a locking band on the outside that blocks accidental activation of the saw. It is important to monitor the condition of the lock very carefully, because improper use can lead to both tool breakage and personal injury.

Fuel equipment

The device is made up of three components:

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Fuel flows from the tank through a hose to the fuel mixing unit, bypassing the gasoline filter (it is located at the end of the pipe, which is immersed in gasoline). To make starting easier, every chainsaw’s fuel system is equipped with a manual pump. It delivers gasoline directly to the carburetor, which helps start much faster.

expensive varieties of saws have a mechanical pump that works together with the cranking of the starter. To return the excess, a tube is attached and directed back into the tank.

Gas Cleaning

To obtain a quality mixture in the gasoline engine, it is necessary to remove excess vapors. This function is performed by the pre-filter and fine filter parts. Also, in cold weather, an additional element is installed to block snow. But this structure is made up of a very dense material, which has a negative effect on performance. At other times, standard filters made of kapron, foam rubber and similar materials are installed. The exhaust is removed by turning the flywheel, which discharges the vapors through a special nozzle. Regular checking of this structure is essential. Otherwise it will cause a decrease in performance.

Starter Design

It is made of a reel with a cable, a return spring and a housing. Such a set is attached to the crankshaft so that when the handle is pulled sharply, cranking occurs. Then a spring returns everything to its original position. The engine can hardly be started at the first try and requires some physical effort.

But it is possible to speed up the procedure by enriching the system with a mixture from the petrol tank. Also this cranking allows you to get a spark through which the ignition. To stop it, you just have to push the stop button.

The cutting chain stops

The chainsaw is a high-risk appliance. That’s why a chain brake is needed here. It is needed to stop in case of a strong impact, which is likely to throw the device into a person. It also stops rotating if the chain breaks in the course of impact. This is called the inert brakes. But there is another (manual) kind of brake. It helps to stop cranking by acting on the corresponding handle. It should be noted that before sawing, it is important to check the quality of the brake tape. Using a saw with a faulty stopper is dangerous to your health.

Check the ignition system

The first thing to do when the chainsaw breaks down is to inspect the spark plug by disconnecting the wire and carefully turning it out with a special wrench.

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

The spark plug is unscrewed to check its condition

How To Replace a Chainsaw Fuel Filter

  • Dry. Most likely the fuel mixture is not getting into the cylinder. It’s not the ignition system, so the spark plug is screwed back in.
  • Highly splashed with fuel. The reason for the excessive fuel mixture is either a violation of the starting rules or improper carburetor adjustment. Wipe the spark plug thoroughly, cut off the fuel supply and turn on the starter. to remove excess fuel and air out the combustion chamber. Then replace the spark plug and restart the machine.
  • Black sludge on spark plug. It could indicate use of bad oil, a carburetor that is not properly adjusted, or an improperly calculated gasoline to oil ratio. Clean the spark plug, remove the carbon deposits with a sharp object (an awl or a needle), rub the electrodes with a sandpaper and return it to its place.

Checking the spark plug, you need to pay attention to the gap between the electrodes: the normal value is from 0,5 to 0,65 mm. A damaged or worn gasket should be replaced.

If there is a lot of black carbon on the spark plug, it indicates a problem with the engine

To be sure, check for sparkling as well. To do this, put the ignition cable on the plug, connect the nut of the plug and the cylinder with pliers, start the starter and watch for sparks. If it is missing, the spark plug must be replaced. If the new spark plug also fails to produce a spark, the problem is in the high voltage wire or a loose connection to the spark plug.