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Chainsaw Carburetor



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The purpose of the chainsaw carburetor is to monitor the fuel and mix it successfully with the air that enters the engine. This enables smooth operation of the chainsaw. A chainsaw carburetor is a relatively simple part of the chainsaw and has 3 basic working functions.


It needs to work when starting the chainsaw engine cold, has to work when the chainsaw engine is idling and has to work when the chainsaw engine is operating at speed.


A chainsaw carburetor that does not function correctly can cause all sorts of problems, so it is essential that the chainsaw carburetor is properly tuned and adjusted. If not enough fuel is mixed with the air the chainsaw will run lean. This means that the chainsaw will not run at all or if it does there is the potential for engine damage. If too much fuel is mixed with the air then the chainsaw engine will run rich.


The results here will be excessive smoke, stalling, in proper running and maybe no running at all. So as simple as the chainsaw carburetor is, it must always be tuned correctly.







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Chainsaw Carburetor Tuning And Adjustment







The majority of chainsaw carburetors will have 3 adjustment screws.


Idle Speed


This adjustment screw is set to control how much the throttle valve will stay open when the actual throttle lever is released. If this setting is too low then the chainsaw will cut out when the throttle is released. This is because no fuel mix will reach the engine. If the idle speed is set too high the chainsaw will continue to run when the throttle is released. This can prove to be extremely dangerous.


Low Speed


This screw controls the amount of fuel in the fuel mixture at idle speed. If too much fuel is allowed the engine will load up and then stop at idle speed. If the setting is too low then the engine will be starved and it will race or surge at idle speed.


High Speed


This screw controls the amount of fuel at cutting speed. This in our opinion is the most important setting of the three. A too high adjustment here will not allow the chainsaw to reach the rpm levels it requires to cut efficiently. The response to the throttle will be sluggish and there will be excessive engine smoke. A too lean adjustment will let the chainsaw reach a rpm level where bearing failure and cylinder seizure are likely to occur. There will be a lack of power in the cut and the chainsaw will run very hot.



To Care Is To Share

Carburetor tuning is essential and critical with the chainsaw and most 2 stroke engines. If the adjustments are carried out incorrectly, problems will occur. If for example an adjustment is too rich the chainsaw will smoke, have insufficient power, experience excessive carbon build up and in severe cases damage the engine. A too lean adjustment will give the chainsaw insufficient power and may even seize the engine. So you can see that it is important to get he carburetor adjustment just right. A finely tuned carburetor will ensure that a chainsaw will produce maximum power, have a longer lasting engine, produce little smoke, idle well, rev perfectly and give the user trouble free service.


An over rich carburetor tuning is where too much fuel is mixed with the air and the fuel does not burn well. Not enough heat is produced with the burn so the power stroke is weaker. This partially burned mixture is forced in to the muffler and then leaves the chainsaw as smoke. Carbon is also a by product.


An over lean carburetor tuning is where too little fuel is mixed with the air and there is not enough fuel to burn. This too makes a weak power stroke resulting in the chainsaw having insufficient power. One main cause of damage from this situation is the cylinder temperature rising and eventually seizing.





Chainsaw Carburetor Adjustment Screws




Preparation For Chainsaw Carburetor Adjustment




Before adjusting the chainsaw carburetor a couple of procedures need to be followed first.

You need to check the air filter. If the air filter is dirty and clogged it must be cleaned or replaced. Attempting to adjust a carburetor with a dirty air filter is like adjusting a carburetor with the choke on. The result will be a chainsaw that runs too lean when the air filter is actually cleaned or changed.


You need to check the muffler. The muffler and exhaust port can become victim to carbon build up. This carbon build up can actually cause a chainsaw to run as if the carburetor needs adjusting, even if it doesn’t. If you adjust the chainsaw carburetor with carbon build up present, the chainsaw will again run lean when the carbon build up is eventually cleaned out.


If you have a new carburetor then you should begin with the fuel adjustment settings one turn out.


Check the fuel levels. You want the chainsaw fuel tank to be at least half full. If you adjust a carburetor with a low tank of fuel the carb may be adjusted too rich when there is a full tank.


Always start the chainsaw up and warm the engine before adjusting the carburetor. Any carburetor adjustment made with a cold engine will result in a too rich mix when the engine warms up.



Adjustment And Tuning



Setting the idle speed. What you want is a speed of about 2600 rpm. You will need a tachometer to do this precisely. However if you do not have one then simply set the speed so that the chainsaw idles as high as possible without the clutch being engaged. Never in any situation set the idle speed so that the chain runs as soon as the throttle is released.


If you find that your chainsaw will not idle you need to set the low speed fuel adjustment. You do this by turning the screw slowly until the engine surges. Remember the position of the screw. Then slowly turn the adjustment screw out. The engine should now run better. Keep turning the screw until the engine loads up. Remember this position as well. The best idle setting position should be between both of the screw positions you have memorized. After this reset the idle speed again in the fashion as suggested earlier. To set the high speed fuel adjustment hold the throttle wide open and check the rpm.


Check your low speed adjustment to still see if it works as well as before you adjusted the high speed screw. It needs to be remembered that changing adjustments on one screw will more than likely affect the other screws. All have to be adjusted simultaneously to get the perfect tune up.