On trimmers, in addition to electric motors, gasoline internal combustion engines are installed. This mechanism requires special attention, because if configured incorrectly, it will either refuse to work or will work intermittently and loss of power. Basically, adjusting the engine is to adjust the fuel supply, and this is done using the trimmer carburetor.
How is the gas trimmer carburetor arranged and working
All varieties of carburetors produced by manufacturers of gas trimmers are almost impossible to cover. But, since the design of this module, as well as its operating principle, is largely similar between different models, a generalized description of the processes occurring in the carburetor can be made. This information will allow the user to understand the principles of operation of the device, eliminate the problems that have arisen and operate it correctly.
The basis of the carburetor trimmer is solid aluminum housing. Below is a diagram of this unit.
At the bottom of it is a diffuser, which is also called venturi nozzle (18). Air is sucked in by the motor through this nozzle.
The smaller this hole, the faster the air flows, and the higher the level of its rarefaction in the zone with the smallest diameter.
At the top of the diffuser are fuel channels (11.12). Through these channels, the flow of air draws in gasoline. The fuel pump itself, the jets and the system used to control the flow of the fuel-air mixture can be built-in or installed externally.
Throttle (9) adjusts the amount of air drawn into the carburetor. Its amount affects the power that the engine develops. The damper (7) is used for cold start. It must be closed if you intend to start the unit. After the engine has started, it needs to be opened, otherwise, the motor will immediately stall.
Pulse channel (1) connects the impulse chamber of the pump to the crankcase, namely, to its internal volume. The piston located in the cylinder, making a reciprocating motion, successively changes the pressure in the crankcase (vacuum or pressure increase). Pressure drops make the membrane move (4). Therefore, the operation of the pump is synchronized with the operation of the engine.
It is precisely with the participation of gasoline leaking from the tank membranes (4). Gasoline enters the carburetor through the fitting (2). Further, its path lies through the inlet valve (3), the exhaust valve (5), through the strainer (6), the fuel channel (10), passes by the needle (14) and fills the chamber (16) having a control membrane (18).
The valve (14) by means of a lever (17) is connected to the membrane (18). The cavity, which is located below the membrane, is connected to the atmospheric air through the hole (19).
The device operates as follows.
- A vacuum is created in the diffuser during the suction stroke. This fact causes air leaks. The position of the throttle (9) determines the amount of air entering the carburetor chamber, as well as engine power and the number of revolutions.
- At this time, fuel from the chamber (16) is sucked through the jets (11,12), after which it is mixed with the flowing air. Gasoline, mixed with air, begins to spray. Thus created air fuel mixture.
- The finished mixture enters the cylinder, where it is compressed by a rising piston and ignites at its correct point from the spark generated by the spark plugs.
- Since the volume under the control membrane (18) is connected with atmospheric air through the channel (19), the membrane goes up, opening the valve (14) by means of the lever (17). After opening the valve (14), a new portion of fuel enters the chamber (16).
- After the chamber (16) is full, the membrane (18) returns to its original position, and the valve (14) closes.
Further, when the motor is running, all of the above processes are repeated. To adjust the amount of fuel entering the diffuser through the nozzles, a screw (13) is used. A screw (15) is also used to adjust the idle speed. When the regulators are twisted, the fuel mixture is enriched, and when twisted, the mixture becomes lean. Also, in some models of carburetors, you can adjust the engine idle quantity regulator. It is usually located outside and, when twisted, rests on a lever fixed to the axis of the throttle.
Thus, using 3 adjusting screws, it is possible to achieve maximum engine performance, as well as to configure its smooth operation at any ambient temperature, and even in mountainous areas.
Common carburetor malfunctions
Damage to the trimmer carburetor occurs due to the use of poor quality gasoline, a damaged air filter and the accumulation of dirt in the chamber of this unit. Most often, it is quite possible to repair a carburetor with your own hands. The following are typical malfunctions of the carburetor lawn mowers.
Fuel pump problems
A common malfunction that “chases” the fuel pump is pump membrane deformation. For this reason, it does not fit properly and the pump channels are not sealed.
The causes of membrane deformation can be as follows:
- long operation of the trimmer;
- use of unsuitable fuel;
- gas entering the pulse channel.
As a result, damage to the membrane reduces the performance of the pump, and as a result:
- there is a depletion of the combustible mixture;
- difficulty starting the engine;
- there are interruptions in the motor;
- the piston is damaged.
Also, the aforementioned consequences for the engine may cause clogging of the pump cavity with impulse side. In this case, dirt enters the membrane through the pulse channel.
To eliminate clogging, you will have to disassemble the carburetor and clean the membrane.
Video: How To Clean A Huter Trimmer Air Filter
The strainer may become contaminated when contaminated fuel enters through a fuel hose or defective suction head. In the photo below you can see what a clean filter looks like and dirty (the parts are separated by a dash).
A thorough cleaning and rinsing of the strainer will be required to resolve the malfunction. Also recommended blow with compressed air all openings in the trimmer carburetor body.
Adjustment lever defective
This failure occurs when the contact surface of the lever wears out.
The contact surface is erased due to the presence in gasoline abrasive particles or due to strong vibration of the motor during operation. This defect of the adjusting lever causes problems with the inlet, as well as improper engine idling.
Inlet needle wear
The intake needle fails, usually due to the presence of abrasive particles in the fuel fluid.
- the tightness of the seat of the inlet needle is violated;
- leakage of the combustible mixture appears;
- there are malfunctions in the engine, associated with the re-enrichment of the fuel mixture.
Also, the inlet needle can simply jam.
Jamming the inlet needle may cause the presence of dirt in the fuel, or a long simple machine without work.
Clogged control cavity
If dirt accumulates in the adjustment cavity, the inlet needle cannot close the hole tightly and a lot of fuel is poured into the chamber.
It causes re-enrichment of fuel, and the engine starts to malfunction. It is necessary to disassemble the carburetor and clean the cavity of the adjusting membrane.
Adjustment membrane deformation
The membrane can undergo deformation during prolonged operation of the unit and when using aggressive fuel.
The impossibility of normal adjustment due to a defect leads to:
- piston damage;
- difficulty starting;
- depletion of fuel;
- engine malfunction.
Inlet Adjustment Lever Problem
This problem may occur if the adjusting lever is not installed correctly, or bend it before installation. As a result, the contact surface takes the wrong position, which disrupts the additional fuel supply.
Throttle and air dampers mostly wear out due to the presence of abrasive particles in the air. Defective flaps look like they were sandblasted.
As a result of wear of the dampers, engine performance decreases, malfunctions appear in its operation, piston rings, piston and cylinder cover wear out.
Throttle and air damper shaft wear
The air and throttle shaft may wear out for the following reasons:
- insufficient and improper maintenance of the air filter;
- the air filter is damaged;
- The air filter is not suitable for this unit.
Due to hit poorly cleaned air, The shaft wears out and may break. Broken parts of the shaft can enter the combustion chamber or crankcase and cause serious damage to the entire piston system.
To eliminate problems with air purification, it is necessary to replace the defective filter or rinse the existing one (serviceable). The filter must be washed in soapy water and dried.
When to adjust
Carburetor adjustment is necessary in the following cases:
- the new engine was tested (4-5 liters of fuel mixture were used);
- fuel composition has changed (brand of oil and gasoline);
- the weather has changed (it has become hot, cold);
- rarefied air (applies to mountainous areas);
- after prolonged storage;
- increased engine load (after changing tools, etc.);
- due to vibration, the adjustment screws spontaneously unscrew;
- increased fuel consumption, carburetor overfills fuel;
- carbon deposits quickly appear on the spark plug electrodes (while the fuel mixture is prepared correctly);
- the engine starts and immediately stalls or picks up poorly;
- no gas enters the cylinder;
- a large amount of exhaust gas.
How to adjust
Before setting up the trimmer carburetor, do the following:
- flush the engine;
- replace or clean the spark plug;
- change to a new one or clean the air filter (it is recommended to wash it in warm, soapy water, squeeze it out and let it dry well).
Also necessary set cord suitable diameter in the trimmer coil or install knives. this is done so that during the tuning process the engine has at least some kind of load. After installing the cutting tool and starting the gasoline engine, let it warm up for 10 minutes.
If at idle You noticed that the cutting tool rotates, therefore, it is necessary to reduce the engine speed. This is done using the lower idle control, often marked with the letter “T”. The figure below shows the placement of the knobs on the Husqvarna trimmer.
But, for example, on a Stihl trimmer, this screw may be labeled “LA”.
So, turn the idle speed control to the left, until the trimmer head stops completely.
To adjust the carburetor, 3 regulators (screws) are used.
- Right knob L adjusts the level of enrichment of the combustible mixture at low speeds. It needs to be regulated first. Get maximum idle speed. This is done using the L knob, turning it left and right. After finding the point of maximum revolutions, return the regulator half a turn to the left (counterclockwise).
- Lower T knob (LA) used to set idle speed. By turning it to the left, the engine speed will begin to decrease, and when you turn the regulator to the right, the speed will increase.
- Left knob H responsible for the enrichment of the combustible mixture at high speeds. The enrichment setting completes the carburetor adjustment. Also, using this controller, you can adjust the maximum speed, fuel consumption and engine power.
Important! If the engine is allowed to run at full speed for more than 10 seconds, then it may fail.
To eliminate this trouble, adjustment will be required. With the engine running, give full throttle, then turn the “H” knob to the right until the reduction in speed begins. After that, the “H” knob must be slowly turned to the left until you hear the engine running unevenly. Then turn the “H” knob to the right until the engine runs smoothly.
After carrying out the above steps, the carburetor adjustment can be considered completed. After proper adjustment, the engine must confidently gain revolutions, slightly quadruple at maximum revolutions, and when idling, the cutting tool should not rotate. This manual is suitable for adjusting carburetors on the Huter, Patriot, and others.
Also exist screwless carburetors, responsible for the enrichment of the combustible mixture at low speeds. That is, they have only 2 adjusting screws: the idle speed regulator and the fuel mixture quality regulator at high speeds. You can learn how to tune this type of carburetor from this video.