Why the grass trimmer does not develop speed

STIHL grass trimmer does not provide enough rpm

The modern market offers a wide range of electric and fuel-powered trimmers from different manufacturers. Machinery may malfunction. For example, insufficient RPM. There is no need to panic about this, as the problem of insufficient revolutions in gasoline mowers, trimmers is quite common. There are several reasons for this.

There are five main reasons why your STIHL grass trimmer won’t rev up:

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Use of low quality fuel

The gasoline trimmer does not pick up if the fuel is of poor quality. It may stutter or not start at all. To check the fuel quality, it is necessary to inspect the plugs. They are the main indicators of problems with the combustion chamber.

If there is a sludge or a fur coat on the spark plugs, pour the fuel from the previous tank off and add a new quality fuel.

It must be remembered that grass trimmer or lawn mower must be filled with good quality gasoline and the brands of fuel specified in the technical passport of the device.

To recap! The spark plugs should be thoroughly cleaned of plaque, and only after that should they be placed back in the combustion chamber.

Stihl Trimmer doesn’t run at full speed.

Contamination of air or fuel filter

If a lawn mower does not pick up speed, the reasons may lie in the contamination of the filter element: air or fuel element.

When the air filter is clogged, there is a lack of oxygen in the combustion chamber, so the fuel is not fully produced, which prevents you from developing the desired speed and power.

To check if the cause is really in the air filter, you need to take it off and turn it on. If the mower is still not picking up the pace, the reasons are not. Then you should check the fuel filter element. Everything is similar here, only in the role of oxygen is gasoline. If this filter is damaged, there will be a lack of fuel, which inhibits the development of the revolutions.

In both cases, the solution is simple: you just need to replace the filter. If you have a spare, install it, if not, buy it at any specialized store, it is inexpensive.

Problems with spark plugs

When the gasoline trimmer is used frequently, it is necessary to monitor the condition of the spark plugs. This part is subject to wear and tear, so they need to be regularly inspected: whether there is no fouling on them.

You can solve the problem in two ways: clean the old spark plug from cinders or buy a new one.

In the first case you need to unscrew and scrape with sandpaper, dry. The distance between the electrodes should be 1 mm. The grass trimmer is assembled and started.

If there is no spark between the electrodes, it is worth checking the quality of all connections. If even in this case everything is normal, it is 100% necessary to change the spark plugs.

It’s easy and inexpensive to replace. Of the tools you will need a wrench, an overhead grinder.

Important! If you often see soot on the spark plugs, it is worth to look for the cause a little deeper.

Remove deposits from spark plugs thoroughly

Engine trouble

Engine trouble is more serious. Several variants of the problem are possible:

In the case of the carburetor problem, you should pay attention first to the condition of the cable. It could be loose, and that’s what caused the malfunction. A simple cable adjustment is needed here.

If this does not help, you need to check the parameters of use. The specified operating conditions can be found in the machine datasheet. Sometimes it is enough to disassemble the device: wash, clean and assemble.

Note! The problem with the carburetor can be solved by purchasing a new element or going to the service for professional services.

The trimmer drive is subjected to a complete check only if the manipulation with the carburetor did not give the proper result.

Failure in the fuel circulation system

Lack of fuel circulation in the system can also be the reason why the unit does not pick up. There are several options for why this happens:

Troubleshooting can be done on your own. To do this, you need:

  • Remove clogs from the gasoline pump;
  • Renew hoses, pipes for fuel circulation;
  • clean the muffler and the mesh on it;
  • install a new catalytic converter.

You should not worry if you have these problems. This does not at all mean that the unit is of poor quality. If a Patriot weed trimmer does not pick up speed, it can be repaired with your own hands and without calling a service center.


The engine starts with great difficulty, the traction is practically absent. The owner swears that everything is new (do you know the symptom too).

In such cases first of all it is necessary to check the spark, the ignition advance angle, the carburetor, the rubber pads under the carburetor (often and densely pads are burst and through cracks air starts sucking) and on any case the air filter. If nothing suspicious in these devices will not be found. measure compression in the combustion chamber and if it will be lower than 8 kg/cm. courageously dissect the piston

In our case, a new piston, so we will not measure the compression, and immediately take off the head and see how things are. And things are neither good nor bad: new parts are so ugly, before buying them you should think twice.

The new head was crooked and it was losing a lot of compression. The case was further complicated by the fact that the cylinder liner is pressed flush with the cooling jacket. With time the liner was a bit warped, just a tenth of a millimeter, so the already crooked crown was leaning on the jacket in one place and there was a big gap between the liner and the liner.

Indirectly the presence of oil under the combustion head can tell about depressurization of the combustion chamber. You see how much oil there is How can you drive like that and still wonder why the engine won’t start?? How can it start if all the compression has escaped through the leaks?

The white cones around the shell show how the head fit into the jacket, and it did fit quite well, 6 mm in some places

Dark spots on the plane of the head indicate a leak. These were the ones that were leaking. The problem is really not that serious: Lubricate the cylinder head and forget about the problem forever

Where the head is good, there’s not even a hint of oil: everything is clean

How much does a tractor trailer weigh?? It is clear that the thermowell will warp from the heat and the head will not provide a tight joint: in our case, the thermowell on one side is a little bit sagged. On native cylinders the liner was sunk into the jacket and the head rested only on it, and in this obscenity is done piggybacked

the original cylinder has a liner that is sunk into the jacket and the joint only rests on it

Diagnosing and troubleshooting gasoline engine problems

Before you start repairing your carburetor, you need to determine the nature of the malfunction. The step-by-step diagnostics and elimination of the arisen problems. further.


This mechanism is an important component of the gasoline trimmer. For the carburetor to work properly, it is necessary to observe several conditions:

  • occasionally disassemble and clean it;
  • Adjust the idle speed according to the manual;
  • seek the assistance of a master adjuster.

In the case of a breakdown of this node, its repair can be done by yourself, but only if you have some knowledge.

One of the causes of poor carburetor operation is a loose cable. To fix the problem you must first disassemble the entire unit, and then, after thoroughly washing all the parts, lubricate and tighten the cable, but not very much, so that it is not tight.

Important! Other malfunctions can also adversely affect the operation of the carburetor: failure of the inlet needle, deformation of the diaphragm, wear of the regulating lever, contamination of the regulating cavity, wear of the sliders.


If there is a problem with the spark plug, it is sometimes enough to dry it or sand it with sandpaper and return it to its place, setting the gap properly. it should be 1 mm. If the spark plug is severely soiled, it is best to use a new spark plug. If the grass trimmer is operating optimally, the spark plugs do not fail very often.


The air filter is blocked and this is another reason for malfunctions. To check the involvement of this element in the malfunction, you need to start the mower without it. A dirty filter can be rinsed in gasoline, dried, or replaced with a new one.

A clogged fuel filter does not allow fuel to enter the cylinder, and the engine stops at full throttle due to a simple lack of gasoline. This element is located inside the tank on the intake hose. To correct the problem, put a new filter on the hose instead of the old one, or thoroughly flush the one that was removed.

Tip! If you try to remove the plug in the tank, the hose and the filter may fall into the tank. It can be removed with a pair of tweezers.


The engine is the most important part of any vehicle. There are several causes of internal combustion engine failures:

  • Wrong proportions of oil and fuel (for two-stroke engines);
  • Stale fuel mixture;
  • Wear and destruction of piston rings;
  • scratch marks on the cylinder and piston;
  • Operating the machine with wear and tear.

All of these things lead to the engine either not starting or stalling.

Important! If all other parts and assemblies of the grass trimmer can be repaired with your own hands, then you need to be extremely careful with the motor. It is better to entrust this work to a specialist. The piston, packings, cylinder and rings can be repaired.

Fuel system

The function of the fuel system is of great importance for the trouble-free operation of the gasoline-powered trimmer. Gasoline passes through the system and must be cleaned regularly. In addition, it is necessary to use only high-quality fuel. For the preparation of the combustible mixture into the two-stroke engine can not be used motor oil, because it has insufficient qualities.

Crash mode

In addition to the DPDZ and DPPA, engineers lay a number of individual form factors, forcing the ECU to put the engine into emergency mode. Others include:

  • malfunction of the camshaft position sensor;
  • Incorrect operation of the variable valve timing system;
  • Invalid signal from the fuel pressure sensor in the diesel engine frame, no signal from the fuel pressure regulator;
  • malfunction of EGR, intake manifold damper actuator;
  • breakage of absolute pressure sensor, air flow meter, etc.п.

If during self-diagnosis, the ECU detected a malfunction that, in theory, could affect the safety of the engine, the power is programmatically limited, the number of revolutions is reduced to a safe level.

Immediately after starting the engine

The machine may stall immediately after starting if the carburetor is misadjusted or has been misadjusted. this causes irregular fuel supply

The result is that the unit begins to vibrate distinctly. To correct the problem, the carburetor is readjusted, acting on the instructions to the mechanism.

Also the engine stops when there is clogged valve

, fuel feeder. In these cases, it is sufficient to simply clean the carburettor. If the lawnmower initially started, but then immediately stalled, it is possible that the fuel to the carburetor unit comes with some difficulty. The problem can be solved by loosening the valve, which allows the mixture to circulate freely in the system.

Stopping can also be caused by air suction

in the presence of mechanical damage to the hose (holes, cracks), which produces fuel intake. In this case, you should add revolutions to the drive to expel air bubbles from the system faster.

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Why the chain saw won’t start?

Almost all systems and components of the gasoline-powered tool are activated during start-up. RPM problems may occur at startup and can be caused by the following:

  • Engine malfunction due to wear and tear or deformation of piston rings and cylinder;
  • Problems with the coil or spark plug. there is no spark to ignite the fuel mixtures;
  • Unbalanced carburetor screws.

To test the ignition module perform the following steps:

  • The spark plug is unscrewed;
  • Its condition is assessed. It must not be covered with gasoline or have a black deposit;
  • The distance between the coil and the magnets is checked (to 0.2 millimeters);
  • In addition the spark plug unit can be checked for sparking by a working mains drive.

If you still can’t get the chainsaw to revs, you should check the carburetor. Low and high rpm are set by default and must be re-set after the run-in period and when the tool is used for a short time.

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Adjust speed with the screws, turn them all the way out. In this situation it is necessary to change the setting of the “H” slide valve, which is responsible for the application of the machine at load. Adjustment of the fuel mixture during engine operation at the highest chain speed. The tachometer and the manual from width=”554″ height=”330″ will help to make the adjustment

How to use and store the lawnmower

To ensure that the lawnmower continues to run properly in the future, it must be stored and operated in good conditions:

  • During operation, keep a close eye on the cooling system, thoroughly and timely clean the channels in the body, as well as the starter ribs;
  • if necessary, use solvents, kerosene and other detergents to clean it;
  • do not clean the tool “hot”. let it cool down;
  • Always follow the operating instructions carefully or you risk overheating the engine;
  • if you do not plan to use the mower in the next month, the fuel mixture should be drained from the mower, t. к. Over time, it breaks up into heavy fractions which will definitely clog the carburetor passages;
  • after draining the fuel, let the trimmer run at idle until it stops, this will help remove any residual fuel mixture.

Before winter storage, do the following steps:

  • completely disassemble the scythe, rinse and clean all the parts you can;
  • Inspect parts for damage and correct misalignments, cuts, bends and any other irregularities as necessary;
  • Pour enough oil into the gearbox and clean the air filter;
  • you can partially disassemble the motor, flush, purge and lubricate all moving parts;
  • To lubricate the piston, unscrew the spark plug, lift the piston to its dead center with the starter, pour some oil into the spark plug hole and crank the crankshaft a couple of times;
  • if you keep the mower out of the house, wrap the engine with an oiled rag.

Remember, by following the rules carefully, you can forget about the lawn mower starting badly for several seasons.

Lawn mower won’t start, spark is gone

Lack of spark entails checking the contacts and the correct gap between them, the wire to the spark plug and the spark plug itself. The way to check the spark plug. unscrew the plug, connect a wire to it, put the plug sideways to the hood of the engine and several times to pull the starter, as if winding up the lawnmower, while you need to look at the angle and the plug contact, between them should run a spark. If you get no spark, take a new spark plug and do the same procedure. If you still can’t find the spark, it is either in the wire or the plug contacts.

When accelerating

In cases where the chainsaw stops when the person presses the gas, the muffler and fuel filter should be checked. Possible cause of malfunction is a leak in the fuel hoses. In some cases it helps to add revs.

Sometimes checking all the parts doesn’t help, the instrument suffocates, stalls when you add gas. If the machine stalls when you accelerate, there may not be enough fuel to work properly. This phenomenon occurs because of a clogged carburetor or filter.

Dust might also contaminate the air filter and cause a malfunction. When you give gas, the device stops working. It is not worth troubleshooting on your own, since each model has its own characteristics.

Insufficient or no lubrication of chainsaw chain can cause a problem. If the chain is dry, it is necessary to clean the ducts through which oil flows to the bar. If the oil leaks, there are cracks, defects on the pipes, you need to treat them with sealant.

Lawn mower won’t start after winter

In such cases you need to service the machine. Take off the fuel system, including filters (air, fuel), disassemble the carburetor, clean and rinse every node. Blow out filters with air

Pay attention to fuel quality and octane rating

Note that products from famous brands like STIHL, Husgvarna and others will not work on cheap gasoline with a low octane rating. AI 92 or higher grade fuel from a gas station is better suited for these chainsaws, but only from a wellproven fuel station, because gas stations sometimes have bad gasoline. The use of high octane and high-quality gasoline will determine how long you will use the mower and how long it will last.

Another problem is the storage of diluted fuel which reduces the working capacity of the mixture and may even lead to a mower that will not start. You have to dilute the mix in portions. in other words, the quantity of mixture which is produced at one time. The instruction manual clearly describes and explains the mixing ratio of gasoline and oil. Strict adherence to the correct proportions will at least save you from several questions, why the lawnmower does not start and what to do in such cases.

Maintenance of gas trimmer parts to prevent the problem

To avoid unnecessary disassembly of the brushcutter, it is worth to diagnose each area separately. the problem may be in one or more parts. Where to look and what to check


One of the main assemblies of a properly working grass trimmer. For the part to function as required, adhere to the conditions:

  • Remove and clean the part every month;
  • Set the idle speed according to the manufacturer’s manual;
  • If you can’t adjust it yourself, take it to a mechanic.

One of the popular reasons for engine failure is the carburetor cable is loose. To fix the problem, first disassemble the carburetor, clean it, and then tighten the cable. Just do not overdo it, so it does not pull on the cable like a string.

It’s also worth checking: the inlet needle, diaphragm, adjustment lever, throttle, and other parts of the carburetor. There may also be problems with the carburettor that prevents it from working correctly.

Spark plug

Even if you don’t know what a properly working spark plug should look like, just take it off, dry it, and sand it down. Put the part back in place.

You can also check the distance on the main part. Maximum. 1 mm gap between igniter parts.

If the spark plug is too black, there is no point in cleaning it. just buy a new one and install it on the motor. The combustion engine is the heart of the gasoline engine. then the whole system is revved up.

Filtration system

A clogged air filter can sometimes affect performance even more than a spark plug problem. To check if it is the problem, start the engine with the filter removed. If it does start, wash the filter sponge in gasoline or other detergent. Or you can buy a new one. your trimmer will only benefit from it.

Clogged filters won’t let the fuel mixture inside the motor, so it’ll stall or won’t start. Lack of gasoline can be corrected by trivial cleaning: both the filter under the cap and the fuel hose filter (located inside the plastic fuel tank).

Engine malfunctions

The internal combustion engine is the heart of your petrol-powered machine. What could be wrong with it if the motor isn’t picking up power:

  • The fuel mixture is not properly prepared, or its expiration date is long gone;
  • The piston rings are broken;
  • Cylinder or piston is scratched and cracked;
  • The machine is being used without interruption.

You should be careful with engine repair. All because if you fix all the parts incorrectly, you can be left without a grass trimmer, as well as with injuries. Leave the job to a professional!