It is important to make carburetor adjustments on chainsaws and this should be correct. With this, the chainsaw can produce maximum power, less smoke, and increase the duty cycle of the engine.
Also, the chainsaw can smoothly get idle, rev up perfectly, and the service will be without any problem. But if there is a rich adjustment, the chainsaw will have a smoke, and less power, due to which there will be more carbon build-up and ultimately, the engine may get damaged.
On the other hand, if there is a too lean adjustment, power will be less and due to lean seizure, the engine may get damaged.
If there is a high proportion of fuel in the combustible air/fuel mixture, the carburetor adjustment is said to be high, and the fuel’s burning is not proper.
With this burn, the heat produced is not enough and thus, the power stroke becomes weak. The partially burned mixture is expelled into the muffler, which ultimately exits from the chainsaw in the form of smoke.
There will be carbon build-up in this condition, and if the chainsaw is run for some time, it can cause a fire screen and cylinder ports. Such situations can even arise when excessive mixing of oil with the fuel or old stale gasoline is used.
The other condition is when the carburetor adjustment is lean and this condition arises due to the low proportion of fuel in the combustible air/fuel mixture. Due to this, the fuel available for burning is not enough and the power stroke becomes weak. As a result of this, there will be insufficient power with the chainsaw, which increases the temperature of the cylinder leading to seizure.
The lean carburetor adjustment can also increase RPM, which fails the big end rod bearing. There are other causes of lean adjustments, like the absence of oil in the fuel mix and when the fuel tank is empty.
Before the complete exhaustion of the fuel, the chainsaw should be stopped. For a chainsaw, the gasoline/oil mixture should be appropriate as recommended. You should ensure that the correct mixture ratio should always be used.
Carburetor Adjusting Screws
In most of the chainsaw engines, there are three carburetor adjusting screws –
1. Throttle stop/ idle speed
This adjustment comes into play when the throttle trigger is released and controls the part of the throttle valve required to stay open. In case this adjustment is too low, then as the throttle trigger is released, the engine will die. The throttle valve will cut the supply of combustible air/fuel mixture, as a result of which the machine will stop working. On the other hand, if the adjustment is high, the centrifugal clutch will get clutched due to the high idle speed resulting in the running of the chain. This should not be allowed anytime as it is a dangerous condition.
2. Low-speed fuel adjustment (the low-speed jet is marked as L on the carburetor)
In this adjustment, the proportion of fuel in the combustible air/fuel mixture is controlled at idle speed. In case the adjustment is too high, the engine will get loaded up, and then at the idle speed, it will die. If the mixture is too lean, the engine will be starved and will either surge or race. The engine can die in this case too.
3. High-speed fuel adjustment (the high-speed jet is marked as H on the carburetor)
In this adjustment, the proportion of fuel in the combustible air/fuel mixture is controlled at cutting speed. This adjustment determines the way the saw runs in the cut. If the adjustment is high, the required RPM level will not be reached by the chainsaw and thus, maximum power will not be attained. There may be sluggish throttle response due to which smoke may come out of the engine and its performance may become poor. If the adjustment is lean, the engine will reach an RPM level where there can be a failure of the bearing, and cylinder seizure can occur. Due to this, power in the cut will be absent and thus, the chainsaw will run very hot.
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The Procedure of Carburetor Adjustment
To have a proper carburetor adjustment, the following procedure should be followed –
1. The first step is to check the air filter and, if required, clean it. If the air filter is partially clogged and the carburetor is adjusted, it will lead to choking of the engine. Also, if the adjustment is made with a dirty air filter, the chainsaw will lean when the filter is cleaned.
2. The muffler and exhaust port should be checked for carbon build-up. The running of the chainsaw can be lean if the carburetor settings are changed with a plugged muffler, especially when the carbon build-up is cleaned.
3. If a new or rebuilt carburetor and adjustment are required, it is advised to start with the fuel adjustment settings one turns out. For this, the adjustment screws should be screwed gently into their seats and then they should be backed one turn each. If the adjustment screws are seated too hard, the seats may get damaged and so, care must be taken while screwing the screws in their seats. If the seats get damaged, the chainsaw user will be required to replace the carburetor.
4. The next step is to check the fuel level. The fuel in the tank should be at least half full. If the fuel tank is empty while adjusting the carburetor, there will be a high adjustment of the carburetor when the tank is filled.
5. Warm the engine by starting it. It should be allowed to run for a few minutes if the chainsaw gets idle. The carburetor adjustment will be too rich if it is done on a cold engine.
6. The idle speed needs to be set up. It should be set at about 2700 RPM. If there is no tachometer, the speed should be set at a level when the chainsaw idles as high as possible without the clutch being engaged. If the saw is not able to get idle, the next step should be followed.
7. The low-speed fuel adjustment has to be set. The screw needs to be turned slowly until the engine starves for fuel. The position of the screwdriver slot should be noted for reference. Now the adjustment screw needs to be turned out slowly and the engine should run in a better way. Until the engine starts to load up, this screw should be kept turning. Now, turn the screw slowly in a position where the engine idles the best. Normally, it is midway between the rich and the lean settings.
8. Now, the saw idle WAV has to be adjusted and for this again, the idle speed has to be reset. It might be possible that there can be a change in the RPM setting due to the optimized fuel mixture adjustment.
9. The high-speed fuel adjustment is to be done. The trigger must be wide open and then check the RPM with the tachometer.
10. It is time to adjust the saw fuel rev WAV. For this, the low-speed adjustment must work and this should be checked. It is found that if adjustments are changed on one jet, the other might be affected. If the acceleration is not as before, you might need to repeat the procedure from step 7.
11. Now, set the final idle speed. During this time, the idle speed screw should be dialed back to the lowest RPM, where there will be a smooth idle of the chainsaw.
After the entire procedure, the chainsaw will be appropriately tuned and will be ready to work.
How to Tune a Husqvarna Chainsaw
A Husqvarna chainsaw should be tuned regularly to get good performance. This even prevents the occurrence of damage due to irregular engines. When the engine is tuned finely, the operations are smooth and for this, three screws on the carburetor are used.
The first screw is the “H” screw which is used to adjust the RPM of the chainsaw during high throttle. The “L” screw controls the low throttle operation. With the help of the third screw, which is the “T” screw, the idle speed can be set when the chainsaw is running, but it has no throttle applied.
1. The air filter should not be plugged with sawdust or any other material and thus, the filter needs to be checked thoroughly. Also, the fuel tank should be at least half full. If these issues are not corrected, the fuel mixture can become rich after adjustment.
2. The engine has to be warmed up and for this, start the engine. Keep it idle for several minutes, during which it will get warm-up. If without stalling out, the saw cannot idle, then squeeze the throttle repeatedly so that it keeps on running. There are chances of severe damage while squeezing the throttle if the engine remains cold or is in the process of warming up.
3. In all these steps, it is required to measure the RPMs, which should exceed the readings mentioned in the manual. For measuring this, the tachometer is required to be attached to the chainsaw. The recommended idle speed in most of the Husqvarna chainsaw is 2700 RPM.
4. By using a flathead screwdriver, the idle speed of the saw can be adjusted. This screwdriver is used on the “T” screw and by tightening this, the richness of the fuel mixture can be decreased. If the screw is loosened, the opposite of this is achieved. The RPMs should not be too high as they may cause the chain to get engaged when the machine is running idle. Also, stalling should not be required for the smooth running of the chainsaw.
5. In this step, tightening of the “L” screw is required, but it has to be done slowly until there is a requirement of fuel by the engine. Make a note of this position and the screw needs to be loosened in the other way until the engine starts to bog due to the rich fuel mixture. Again, this position has to be noted and the screw is to be tightened again until the chainsaw becomes comfortable in being idle. In most cases, this is the position between the two settings.
6. There may be a chance that after adjusting the “L” screw, the optimized fuel settings at idle speed may be changed. For this, the “T” screw must be adjusted again.
7. The chainsaw is to be given full throttle and then the “H” screw needs to be adjusted and tightened. This should be done until there is a requirement of fuel by the engine and so, it starts to bog again. There is a point where the chainsaw runs smoothly between these two points and you need to find it.
8. Now, the throttle has to be released. If any readjustments in the “L” screw are required, make the settings again.
9. For the last time, the idle speed has to be adjusted and return to the “T” screw. At this moment, the chainsaw must run smoothly and so tighten the screw accordingly. Ensure that the chainsaw does not stall on you while adjusting the “T” screw. After doing so, the chainsaw is ready to use.
How to Tune a Stihl Chainsaw
Tuning a Stihl chainsaw is relatively easy compared to other brands as there are only three carburetor adjustment screws in it. The screws present in a Stihl chainsaw are –
1. Idle Speed Screw or LA – This screw helps to control the speed of the engine at idle. The chainsaw will get damaged if this screw is set too low. If it is set too high, the chain will run, but it will be dangerous for the user.
2. Low-speed adjustment screw or L – It helps in controlling the air/fuel mixture at idle. This screw is a low-speed jet. There is a chance of the chainsaw dying at idle speed if this screw is adjusted too rich. The reason behind this is there can be blubbering of the chainsaw due to its adjustment. In case the “L” screw is adjusted too lean, the engine will starve. There will be either race or surge of the chainsaw. Also, the engine will die if the adjustment is extremely low.
3. High-speed adjustment screw or H – It is a high-speed jet that can help control the air/fuel mixture at high RPMs when adjusted. The chainsaw will blubber if the screw is adjusted too rich.
1. First, the adjustment screws H and L have to be turned down clockwise onto their screws. This has to be backed off for 1 complete turn.
2. LA idle speed screw has to be turned until the chain stops. Then for one-quarter of a turn, turn the screw anti-clockwise.
3. Now, it is required to fine-tune screw L.
If the idle setting is too lean, the L screw has to be adjusted. For this, turn it anti-clockwise until the engine’s proper acceleration and the engine runs smoothly. Now, readjust the LA screw.
If the idle setting is too rich, the L screw has to be turned clockwise until the engine’s speed lowers down. Then, for one quarter, turn the screw back. At this point, check if the acceleration of the engine is smooth when the throttle is opened. Now, the LA screw has to be readjusted.
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FAQs for How to Tune a Chainsaw
How do you properly tune a chainsaw?
The following procedure should be followed to tune a chainsaw –
First, start the chainsaw and run it for a few minutes to warm it. Let it idle for several minutes and then pick it up and tip it forward. If the engine stalls, the low-speed screw has to be tightened. With this, the amount of fuel entering the carburetor will be reduced. Now, the idling saw has to be accelerated. If it is not able to accelerate, loosen the low-speed screw. This will ensure an increased amount of fuel enters the carburetor. Again, the idling saw has to be rev for another 5 seconds.
While the saw idles, if the chain is stationary, it means the tuning is complete. But if the chain rotates around the bar, the idler screw has to be adjusted so that the chain stops. Within a few seconds, this situation can be fixed.
In this way, you can easily tune your chainsaw.
How do you adjust the H and L on a chainsaw?
H screw is a high-speed adjustment screw and its adjustment controls the fuel/air mixture at high RPMs. L is a low-speed adjustment screw which when adjusted, controls the fuel/air mixture at idle.
Both these screws have to be turned clockwise until they stop naturally.
How do you adjust a carburetor on a chainsaw?
For adjusting a carburetor on a chainsaw, first, clean the air filter and at least half of the gas tank should be full. When the chainsaw is warm, turn the high and low-speed screws completely in. each of these screws has to be back off to the left in one full turn. Now, the high-speed screw has to be turned clockwise, due to which the fuel mixture will lean out. Finally, the high-speed screw should be turned to the left until you hear a fluttering sound. This is the right RPM for your chainsaw, and the carburetor is adjusted.
There is another way of adjustment in which the throttle is involved. For this, the chainsaw should be idle. It should not be moving. If it is moving, the throttle screw has to be turned clockwise until there is no chain motion.