Chainsaw carburetor adjustment with STIHL MS 250 as an example
The necessity of the operation “Adjusting the carburetor of the chainsaw” is determined by the color of the spark plug electrodes: if black. means re-enrichment, if brick-gray. means the norm, if white coating on the candle electrodes means lean mixture.
The main role in adjusting the carburetor of the Stihl chainsaw is played by the upper screw (closest to the muffler). According to the factory parameters (indicated on the cover of the chainsaw) it must be unscrewed by 1 revolution, and then it must be adjusted. if you unscrew it, the working mixture is enriched (more gasoline enters the air-fuel mixture), if this screw is screwed in, the working mixture is depleted (less gasoline gets into the air-fuel mixture).
Adjusting the carburetor of the STIHL MS 250 chainsaw (with rev counter):
Before adjusting the carburetor of the Stihl chainsaw, it is necessary to carry out maintenance of the chainsaw (cleaning the carburetor of the chainsaw, washing the engine of the chainsaw, replacing the spark plug, cleaning the air filter, checking the chain tension, adjusting the idling speed, warming up the engine).
1. Screw the screws “H” and “L” (on the muffled chainsaw) as far as they will go, and then turn them both out 1 turn.
2. Start the chainsaw and warm it up. Give full throttle and use the “H” screw to achieve a maximum engine speed of 14,000 rpm. by tachometer (by engine speed counter). Maximum revolutions for adjustment to keep no more than 10 seconds!
3. Use the “LA” idle stop bolt to make the chain begin to move, and then turn this bolt ¼ turn counterclockwise.
4. If, after this adjustment of the chainsaw carburetor, the idle speed is not stable, and the chainsaw does not accelerate well, then you need to turn the “L” screw a little counterclockwise until the chainsaw starts to gain speed and work well at idle. Then correct the bolt “LA” (idle tachometer should be 2800 rpm). Attach.
Note: It is not possible to adjust the carburetor of the chainsaw if there is air leakage into the engine from the side (through the gasket under the carburetor, through the accelerator pump of the carburetor, through the oil seals of the crankshaft of the chainsaw or elsewhere).
Video: How to Remove a Carburetor Stihl Ms 180
Adjusting the carburetor of a Stihl chainsaw may be necessary when changing the quality of the fuel, the altitude at which the Stihl chainsaw is used (vacuum), as well as when changing atmospheric pressure, temperature and humidity. Tuning the carburetor of the chainsaw allows you to achieve excellent performance chainsaws with deteriorating external operating conditions. Also, adjusting the carburetor of the chainsaw helps prevent oil starvation and engine breakdown due to insufficient lubrication entering the cylinder with a lean fuel mixture.
Tip: To check the tightness of the engine, it is very good to use a special device, i.e. special pump with pressure gauge. First you need to remove the carburetor on the chainsaw, and install a sealed plate plug with a flange on the inlet window of the cylinder to connect the hose to the pump. The spark plug for tightness can also be put on the sealant. You must also remove the muffler, and install a sealed plate with a rubber gasket on the exhaust port of the cylinder. Then you need to put the piston at top dead center and connect the hose from the pump to the flange. Next, you need to pump air into the engine up to 0.9 atm. and look at the gauge needle. if it stands still, then the piston of the engine is tight. Then we release air, switch the device (pump) and start pumping air out of the cylinder, creating a vacuum in the engine with a pressure gauge reading of 0.5 atm. We look at the pressure gauge needle. if it stands still, then through the gaskets or other seals in the engine there is no air leak (which worsens the operation of the chainsaw and does not allow the carburetor to be correctly adjusted for the chainsaw). Thus, we check the engine for air leakage and compression.
Adjusting the carburetor of the Stihl 180 chainsaw.
1. Standard idle adjustment (abbreviated h.h.): turn the screw counterclockwise until it goes tight, after which we make two turns clockwise, and that’s it.
2. If the engine speed is too low. then you need to turn the screw clockwise until the chain starts to move, and then turn the screw 0.5 turns counterclockwise.
3. If the engine speed is too high. then you need to turn the screw counterclockwise until the chain stops rotating, and then turn the screw another 0.5 turns counterclockwise.
That’s it, the carburetor adjustment for the Stihl 180 chainsaw is finished.
A chainsaw carburetor is a part of the chainsaw fuel system designed for foggy mixing gasoline with air and dosing the supply of this fuel mixture to the engine cylinder.
Note: The chainsaw carburetor mixes gasoline with air in a proportion of 1:14, i.e. 1 part of gasoline with oil is mixed with 14 parts of air, and adjusting the carburetor of the chainsaw ensures the correct ratio of these components of the fuel mixture.