How To Adjust Idle Speed On A Trimmer
The increased fuel consumption and the rapid formation of soot on the lawn mowing candles when using a correctly prepared fuel mixture indicate the need for carburetor adjustment. This describes how to set trimmers with carburetors that have one screw for adjusting the fuel supply.
Flush the air filter before adjusting the carburetor. It is recommended to rinse it after every 10 hours of operation. After that, you can begin to adjust. The example photograph shows the carburetor of the gasoline trimmer PRORAB-8406. The numbers indicate the adjusting screws that we will use.
Prorab-8406 gas trimmer carburetor adjusting screws
Purpose of adjusting screws:
- Fuel mixture adjusting screw.
- Idle adjustment screw.
- The screw limits the maximum speed.
Start the lawn mower and wait until it warms up.
Start slowly tightening the fuel mixture adjusting screw until the engine stalls or stalls unless you catch the moment. Then unscrew the screw a quarter of a turn if the engine is not dead, or half a turn if it is dead. Start the stalled engine. Check, by opening the throttle, how the engine accelerates. Continue to loosen screw # 1 a quarter of a turn until the engine starts to confidently gain high revs when progazovka. This will be the moment of the most economical stable engine operation. At the PRORAB-8406 gas trimmer, the adjusting screws are turned clockwise, unscrewed. Against, for some other brands the lawn mowing may be vice versa.
We proceed to adjust the low speed. Screw number 2 restricts the return movement of the throttle lever. By wrapping it, we increase idle speed, unscrewing. Reduce it. Adjust so that the engine runs confidently at low speeds and even slightly faster (for a better start), but so that the reel with fishing line or knife does not rotate, and before starting to rotate, there is a sufficient margin of speed. If the engine starts poorly, still increase idle speed.
Maximum speed limit
After adjusting the flow of the fuel mixture and low revs, check how the lawn mowing engine will operate at maximum speed. If necessary, limit the maximum speed to the required level using the No. 3 hollow screw. Loosen the locking nut and screw in to decrease the maximum speed or unscrew to increase. After adjustment, tighten the nut. Setting the maximum speed is necessary to protect the trimmer motor from overheating and the ability to use the release key lock to reduce fatigue of the right hand.
In the future, it may be necessary to adjust the trimmer carburetor. For example, if the engine, when operating at full load, starts to pick up revs poorly, loosen screw No. 1 another quarter of a turn. If it is difficult to start, increase the idle speed. Weather conditions and the quality of the fuel mixture can affect the operation of lawn mowers. The vibration can also make the adjusting screws turn themselves.
The spring may interfere
My first attempt to adjust the carburetor of the lawn mowers did not work, as the spring of the fuel mixture adjustment screw prevented it. The factory spring turned out to be too thick in a compressed state and did not give the opportunity to reduce the fuel supply to the required level. I had to pick up another spring and continue adjusting after replacing it.
Spring mixture adjustment screw
In the photo above, the factory spring, below the adjustment screw with a selected spring. I am writing about this, because I’m not sure that this is an isolated case, and someone else may encounter the same situation.
From personal experience
Lawn mowing or trimmer
A trimmer is a broader concept than a lawn mow (lawn mow), since it can also be electric. A gas trimmer and a lawn mower are one and the same.
Some authors claim that the trimmer is a weaker tool, in contrast to the more powerful lawn mowers, which can be used to mow shrubs. Personally, I have a tool with a maximum power of 1.7 kW and capable of mowing a small shrub up to 10 mm thick, as stated in the instructions. The user manual is called “Petrol trimmer”.
Fuel mix ratio
I read somewhere that if in the instruction manual for lawn mowers and on the canister with oil different proportions of the preparation of the fuel mixture are indicated, the proportion indicated in the manual should be used.
It did so for a long time. Excess oil flowed from the engine to the gas tank and soot was constantly forming on the candle, since the manual indicated the proportion for the engine being run in 1:25, and on the canister. 1:50. After the transition to a proportion of 1:50, the appearance of oil drips stopped. The candle continued to burn, but with less intensity (the carburetor was not yet adjusted).
Until now, some users of gasoline tools determine the proportion of the fuel mixture “by eye”. If during the preparation of the mixture the amount of oil is underestimated, after some time an extraneous sound may appear immediately after the engine starts, gradually disappearing during warming up, and the engine stops with a sharp jerk. Continued operation of the trimmer in this mode will lead to its failure.
In the worst days of working with a trimmer with an unregulated carburetor, the engine stopped starting after using each fuel tank. And only after cleaning the candles from soot could we continue to work.
To clean the electrodes, fine sandpaper was used, and to clean the space between the insulator and the body, a thin clerical clip with a bent end was used. First, the electrodes were wiped off with a lot of dirt with a rag, then they were cleaned with sandpaper. After that, the candle was lowered into diesel fuel and the moistened soot was scraped off with a paper clip from the surfaces of the insulator, the inside of the housing and between them. Further, the candle was lowered several times in diesel fuel, which was then shaken off from it along with impurities. Sometimes the cleaning procedure with a paper clip and washing are repeated. After that, the candle was wiped dry and was ready for further use.
Incredibly, one tank of the fuel mixture with an unregulated carburetor can be consumed in less than 10 minutes. It was tested in practice when the trimmer was started and operated at high speeds with maximum fuel supply (the adjustment screw was unscrewed much more than normal).
Lawn mowers, like all gasoline powered tools for the garden, are not difficult to maintain. It is possible and necessary to repair, configure yourself. For example, adjusting the carburetor of the lawn mowers with your own hands is a matter of five minutes.
Lawn mowing 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.
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 acetone or the same gasoline for flushing.
Blowing off carburetor parts with a blockage of compressed air is an acceptable and convenient repair practice.
The device of the carburetor lawn mowers
The basis of the carburetor of the lawn mowers is an aluminum case. It has a diffuser (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 the carburetor lawn mowers
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.