For the small, compact Stihl 250 chainsaw mechanism, proper carburetor tuning is key. All coordinated work, all load conditions and its trouble-free operation directly depend on the adjustment of the fuel supply systems, the quality and quantity of the fuel-air mixture. This article describes how to adjust the carburetor for the Stihl 250 and configure all of its dosing systems.
In fig. 1 shows a modern carburetor for a German chainsaw manufactured by Stihl 250. It is a knot the size of half a human fist. The manufacturer of the movement is Walbro, Taiwan. Case material. stainless steel alloy. At the bottom of the device, a shutter is fixed, providing a uniform supply of the fuel-air mixture to the engine combustion chamber.
Fig. 1. Carburetor for the Stihl chainsaw.
Here, holes are made for attaching the assembly to the power unit housing. Between the flanges of the mixture supply and the combustion chamber of the engine, a gasket is installed. An accelerator pump is located under the throttle rod. It is a small piston with a rubber ring.
On the front of the case is a series of easy-to-use spring-loaded adjusting screws:
- idle move;
- maximum speed;
- amount of mixture;
- mixture quality.
The carburetor of the Stihl chainsaw is adjusted with these screws.
The main innovative feature of the carburetor for the Stihl 250 chainsaw is the heating device. In order to avoid freezing of the mechanism during operation during the winter period, it is equipped with a special system that preheats the steel case during operation. For this, the unit is switched to winter operation.
The body is blown with heated air drawn in from the engine. This mode of operation of the mechanism prevents icing, freezing of the nozzles, provides a normal flow of the fuel-air mixture. When switching to summer operation, the hot air damper closes. Summer mode is characterized by natural cooling of the unit.
Features of the Stihl 250 chainsaw
Throughout the operation process, the need periodically arises for additional adjustment and ensuring the correct supply of the fuel-air mixture. How to determine exactly when and what kind of adjustment is necessary for the normal functioning of the equipment? There are characteristic signs when the mechanism, by the behavior of individual parts, itself suggests when adjustment is necessary.
First of all, each time before the next engine start, it is necessary to check the color of the spark plug electrodes.
By changing it, you can decide on the need for adjustment, adjustment of work processes, improving the quality of the combustible mixture:
- Black electrodes coated with soot or soot indicate a re-enriched air-fuel mixture entering the engine.
- Brick-gray electrodes indicate that the mixture is perfect in composition and no additional adjustments are required.
- White plaque on the candle electrodes indicates that the mixture is lean.
Video: Stihl 250 Oil Pump Replacement
The signs described in paragraphs 1 and 3 indicate that carburetor adjustment is essential for the Stihl 250 chainsaw.
NOTE! Do it yourself, the Stihl 250 carburetor may need to be adjusted by the owner if it has changed: fuel quality, altitude, or if air pressure has occurred at the place of operation of the chainsaw. Perhaps, humidity, temperature, atmospheric pressure has changed.
Exact settings will allow you to achieve maximum unit performance while reducing the external necessary conditions for its operation. Successful debugging of operating conditions prevents oil starvation and engine failure due to insufficient lubrication. After all, the lubricant enters the saw cylinder along with a lean air-fuel mixture.
Preparing for carb adjustment
Of paramount importance when setting all the fuel metering characteristics of the Stihl 250 is the top-most adjusting screw located near the muffler. The factory setting, the parameters of which are shown on the upper plastic cover, provides that it must be twisted one revolution from a full twist.
Do-it-yourself Stihl 250 chainsaw carburetor adjustment is carried out throughout the operation process. Unscrewing the screw enriches the working mixture, since the air-fuel mixture receives a larger volume of gasoline, and twisting the screw depletes the working mixture, since the air-fuel mixture receives less gasoline.
Adjustment of the carburetor will not give positive results if air intake from the engine side takes place through:
- carburetor gasket;
- accelerator pump rubber ring;
- crankshaft oil seals.
Setting up the Stihl 250 carburetor is carried out only after a careful inspection, identifying the existing air leaks. The next stage of preparatory commissioning is the full maintenance of all components and mechanisms.
- cleaning from deposits, slags, resins;
- engine wash using solvent, acetone;
- spark plug replacement;
- cleaning, washing the air filter;
- checking the tension of the cutting chain;
- idle setting;
- engine warming up to operating temperature.
Then you can proceed to complex manipulation settings.
Carburetor Adjustment Stihl 250 Chainsaw
Fig. 2. Carburetor adjustment for the Stihl 250 chainsaw.
Step-by-step adjustment of the Stihl МС 250 carburetor with a rev counter is carried out in the following sequence:
- Switch off the engine, tighten the screws H and L all the way, then unscrew both by one turn.
- Start the engine, warm up. At maximum speeds with screw H, achieve a maximum crankshaft frequency of 14,000 rpm, fixed by a tachometer or engine speed counter. Keep maximum engine speeds for no more than 10 seconds.
- Use the idle bolt LA to start the chain. After that, turn the bolt LA ¼ turn counterclockwise.
- Check the acceleration of the Stihl 250 chainsaw mechanism. Carburettor adjustment continues if the idle speed is unstable or the chainsaw is not accelerated enough. Screw L must be turned slightly counterclockwise. At the same time, the saw should quickly gain momentum, steadily function at idle. Finally, correct the operation with the LA screw. According to the tachometer, the idle speed should correspond to the catalog value of 2800 rpm.
Similarly, you can adjust the carburetor of the Stihl 211 chainsaw with your own hands.
In his article, the author covered in as much detail as possible all the adjustment details of a well-known German production mechanism called the Stihl 250 saw. Carburetor adjustment is simple and accessible to every home master. By following the recommendations made by the author of the article, everyone can customize their Stihl 250 chainsaw and enjoy its flawless performance.
Engine oil for two-stroke engines STIHL 1:50:
1:50 = 1 part oil 50 parts gasoline
other branded motor oils for two-stroke engines of the TC classification: