Stihl 38 Trimmer Carb Malfunction
Gas scythes, like all gasoline powered tools for the garden, are not difficult to maintain. It is possible and necessary to repair, configure yourself. For example, do-it-yourself carburetor adjustment of the brushcutter is a matter of five minutes.
A brush cutter carburetor is a unit in the power system. In it, like any carburetors, there is a process of mixing air and fuel (gasoline) for further supply to the engine cylinders.
In this process, the main thing is the correct proportion of fuel and air, for which they regulate the carburetor.
The main problems and malfunctions of the carburetor.
Strainer There are only two problems with this element:
In order to find out the cause of the breakdown, the fuel filter cover is unscrewed to remove the strainer. If dirt has simply accumulated on it, washing with gasoline or blowing will help.
With visible damage to the strainer, it is imperative to install a new one. There may also be damage on the fuel supply pipe (during repair, check this element).
The carburetor starter in most cases does not function due to blockages. Use rinse with acetone or the same gasoline.
Blowing off carburetor parts with a blockage of compressed air is an acceptable and convenient repair practice.
The throttle body, the bundles of carburetor parts, the intake or exhaust pipe. All of these parts are subject to depressurization. You can probably check it in a primitive way. Smear the problem area with soap suds.
Arboretum carburetor device
The basis of the carburetor petrol scythes is an aluminum case. It contains a diffuser (a hole with internal contours). Air is blown through this hole. The oxygen (air) flow rate depends on the cross-section (passage opening) of the diffuser.
The diffuser is equipped with fuel channels. Of these, fuel is drawn in using an air stream.
Outside the carburetor is installed:
- Fuel pump;
- Jet system;
- Fuel / air mixture control system;
The principle of operation of the carburetor
The throttle valve determines the amount of air for supply, and engine power directly depends on this.
Fuel is sucked into the carburetor system by a pump (its membrane). Then it passes through the fitting in the carburetor. Further, the fluid moves through the inlet and outlet valves of the pump. Filtered by mesh. The needle valve moves into the membrane chamber.
Phased operation of the device:
- Air supply to the tube with an air baffle (damper). The partition controls the intensity of the air flow.
- The fuel supply system must be narrowed by a diffuser to increase the flow rate.
- Gasoline through the float chamber and nozzle tube with narrowing. A camera with a float adjusts the temporary volume of gasoline. In the float chamber, the pressure level is neutral, and in the tube with narrowing is already low. Due to the pressure drop, fuel enters through the nozzle.
- The acceleration of the air flow contributes to the transfer of fuel (gasoline) and its atomization. As a result, an air-fuel mixture of the necessary proportion or density is formed.
- The air-fuel mixture enters the engine cylinder through the fuel pipe.
The level of air density in the system depends on the area of the open air damper. The wider the flap is open, the greater the fuel consumption and power.
Simply put, adjusting the carburetor on the brushcutter is creating the optimal fuel mixture due to the correct air supply.
How to adjust a carburetor on a brush cutter
Before adjustment, carefully clean the filters according to the maintenance in the instructions.
Do-it-yourself carburetor further tuning of the brushcutter is done by adjusting screws. There are three of them:
Right (L). Adjustment of the fuel mixture for low revs.
Need to find the maximum idle speed. To do this, slowly turn the screw (L) to the right and left.
To adjust, turn the screw a quarter of a turn necessarily counterclockwise.
Bottom (T). Is responsible for adjusting the engine at idle.
- Clockwise. Increase;
- Counterclockwise. Decrease.
For proper adjustment of idling, it is typical:
- Steady work of the cold engine;
- Not overestimated speed of the hot engine;
- A large headroom for the trimmer head;
- Stable operation of the engine when changing position (sharp rise or descent of the knife).
Left (N). Adjustment of the mixture at high speeds. (The screw is configured last).
The left-hand screw (N) determines the general adjustment of the maximum speed, engine power, temperature and gas mileage.
The carburetor trimmer with the last screw is configured as follows:
- Open the throttle to full, while giving out full throttle. Turn the screw clockwise until the speed drops (in this case, they are oriented by ear).
- Turn the screw as slowly as possible counterclockwise until the engine runs unevenly.
- Then turn back quite a bit, barely hearing a stable, smooth operation.
- For a more visual application of skills, it is more convenient to consider the work of an experienced user:
Interestingly, from the point of view of the author of the, the setting (its correctness) is determined by the color of the candle, and not just by the speed and stability of the engine.
The correct setting of the carburetor with your own hands in this case is the combustion of the fuel mixture without residue, the color of the candle should be light brown.