What does a Carburetor do on a Chainsaw?
A Chainsaw carburetor is quite simple, as carburetors go, but it is not without intricacies. The purpose of a carburetor is to accurately control the extremely small fuel quantities and mixing it with air that enters the engine so as to make the engine run properly. When there is not enough fuel being mixed with air, there will be lean-burn of the fuel and engine will either not run or will potentially get damaged. A lean mixture is as a result of not enough fuel or too much air. Normally, in a 2-stroke engine such as that of a chainsaw, fuel also provides the engine’s lubricant. When there is, excessive fuel being mixed with air, the engine will “run rich” or get flooded with fuel, and might not start, or will run and emit a lot of smoke, or it will run poorly such that it stalls easily and bogs down, or even waste fuel. Chainsaws that run lean or rich will emit excessive exhaust. Thus, a chainsaw that runs properly will have the proper fuel/air ratio, a healthy spark, and enough compression for heating the fuel-air mixture. The carburetor is responsible for getting the right air/fuel ratio for the mixture.
The carburetor in a chainsaw is relatively simple as compared to other carburetors as it only needs to work in these three situations;
- If you’re trying to start the chainsaw cold.
- While the chainsaw engine is idling.
- When the chainsaw engine is open wide.
Few people that operate a chainsaw are really interested in the gradations between full throttle and idle. Thus, the incremental performances between these extremes is not really significant. However, for larger engines such as that of a car, the many gradations are essential, which makes car carburetors far more complex.
A chainsaw carburetor has the following main features; First, the carburetor is generally a tube. Across this tube, there is an adjustable circular plate known as a throttle plate. Inside this tube, there is a narrowing at some point, and which is known as the venturi. In the venturi is where a vacuum is created. Inside the venture is a hole known as a jet, which allows the vacuum suck in fuel.
When a carburetor operates normally at full throttle, the throttle plate is usually parallel to the tube’s length, allowing for the maximum flow of air through the carburetor. The flow of air creates a vacuum inside the venture, and the vacuum sucks in a controlled fuel amount through the jet.
When the chainsaw engine is idling, then the throttle plate is often nearly closed. In this case, there’s is not enough air flow through the venture to form a vacuum. Nevertheless, on the throttle plate’s back side, there is vacuum since the plate is preventing air flow. Should a tiny hole be drilled into the carburetor tube’s side, the throttle vacuum could suck in air into the tube. The tiny hole is known as an idle jet. There is another screw labeled ‘Lo’ or ‘L,’ and which regulated the amount of fuel flowing via the idle jet.
When you try starting the chainsaw with a pull-cord when the engine is cold, it runs at extremely low rpm. Also, the engine is cold and therefore requires a very rich air-fuel mixture to start. Now is when the choke plate comes into play. When it is activated, the plate will cover the venturi. When the venturi is covered, and the throttle wide open, a lot of fuel is sucked in by the carburetor engine via the main jet as well as the idle jet. This results in a very rich mixture that allows the engine to fire either once or two times, or just run slowly. Now if the choke plate is opened, the engine starts running normally.
How to Adjust the Carburetor on a Poulan Pro Chainsaw
The carburetor of a Poulan chainsaw has a single feature for tuning using a tool for increasing and decreasing the idle speed. The Poulan carburetor is usually set correctly from the factory. However, the adjustment may be necessary when the engine is running poorly, runs at high speed, or dies. An engine running at very high speed could get damaged or run inefficiently. An engine that runs at slow speed then the normal may stall and die, and require restarting often.
Tuning a Poulan carburetor need to be done when the engine is hard to start, dies after starting, or dies when under load. In such situations, the ratio of fuel and oil to air requires being enriched. Should the chainsaw sound as if its engine is running too rich, then it revs at high speed and makes a high-pitched sound. In such case, the fuel-air mixture should be made leaner to avoid damage to the engine.
Before tuning the Poulan chainsaw carburetor, you first place the chainsaw flat level surface in such a way that the chain is overhanging the surface, or all items should be moved away, so the chain doesn’t contact anything. Since the chain moves during the adjustment, you should be wearing protective gear including leather gloves, closed-toe shoes, long pants, long-sleeve shirt, and safety glasses.
Adjusting the carburetor at idle speed, find the idle speed screw marked with a ‘T’ right above the primer bulb. Now start the chainsaw normally and allows it to idle, while making sure that the chain doesn’t reach anything. Using a small flat-headed screwdriver turn the idle speed screw clockwise so as to increase the speed if the engine idles too slowly. When the chain starts moving, turn the idle screw counterclockwise so that the engine idles without stopping and the chain stops for the right idle speed.
How to Adjust the Carburetor on Homelite Chainsaw
Homelite carburetors, just like those of other small-sized engines will often change settings due to regular bumping and vibration during normal operation. Often it is not difficult to note when there is need for adjustment of the carburetor setting. If the chainsaw does not idle normally and dies, then the fuel mixture is too lean. If the chainsaw idles too quick and the chain moves on its own, then the mixture is too rich. In this cases, you need to turn the idle-speed screw and locate the point at which the engine will idle smoothly, and the chain doesn’t move on its own.
Before tuning the carburetor, you should check the air filter for debris and dirt. To access the filter, remove the two screws securing the plastic cylindrical cover of the Homelite chainsaw. Pull off the cover to access the filter. Loosen and remove the screw securing the filter. Tap the air filter on a surface to loosen dirt and dust. Wash the air filter using warm running water and liquid home detergent. Rinse and dry it thoroughly and fix it back onto the chainsaw and tighten the screw that held it. Set back the cover and secure it with its screws.
Adjusting the Homelite chainsaw carburetor involves tuning the idle speed screw. This screw is on the side of the chainsaw right above the starter cord handle. To tune the idle speed, use a screwdriver and insert it into the hole labeled with a ‘T.’ When the engine idles too quick, and the chain moves on its own without the throttle trigger being pressed, then the mixture is too rich and requires to be made leaner. Turn the idle speed screw counterclockwise in ¼ turn increments reducing the engine speed until the engine idles smoothly and when the chain stops moving. If the engine starts and run but does not idle when the throttle trigger is released, then turn the idle-speed screw clockwise. Turn the idle screw in ¼ turn increments such that the chainsaw engine runs smoothly.
How to Adjust Carburetor on a Husqvarna Chainsaw
Place the Husqvarna saw on a flat level surface ensuring there nothing contacting the chain when you will be tuning the carburetor. Start the engine and allow it to run for five minutes to warm. Locate the 3 different adjustment screws that are placed near the start cord on the chainsaw’s body. There is a letter stamped next to every screw. Rotate the screw labeled ‘L’ clockwise using a flat-head screwdriver until the end. Do not turn the screw beyond its natural stop. Rotate the screw counterclockwise such that the chainsaw idles smoothly without stopping. To test the engine, press the throttle trigger. Adjust the screw labeled ‘L’ until the chainsaw accelerates smoothly and sounds smooth.
Place the flat-head screwdriver on top of the idle-speed adjustment screw which is labeled ‘T.’ Turn the screw in a clockwise direction until the chain starts moving. Immediately start turning the screw counterclockwise such that the chain stops moving. The chainsaw should maintain the idle speed while the chain does not turn.
Turn the adjustment screw labeled ‘H’ in a clockwise direction using the flat-head screwdriver to the screw’s natural stop. At this point, the engine sounds very rough. Now turn the screw in the clockwise direction until the engine on your Husqvarna is running smoothly. On squeezing the throttle trigger, the chainsaw should accelerate without difficulty and will not blow smoke from its exhaust.
How to Adjust a Craftsman Chainsaw Carburetor
Before adjusting a Craftsman chainsaw carburetor, you will need to have a small flathead screwdriver and a piece of wood.
Put the chainsaw on a flat level surface and ensure nothing is in contact with the chain. Locate three carburetor adjustment screw found on the side of the fan housing and start cord. The two screws at the top are labeled ‘L’ and ‘H.’ The screw labeled ‘L’ is for low-speed adjustments while the ‘H’ screw is for high-speed adjustments. The bottom screw labeled ‘I’ is for idle adjustments.
Turn the ‘L’ and ‘H’ screws clockwise until their natural stop. Turn both screws on counterclockwise one full turn.
Now start the chainsaw and let the engine idle for two to three minutes. When the engine idles to low or sputters, then slowly rotate the ‘I’ screw in clockwise direction until the chainsaw engine runs smoothly. When the engine idles to high, then slowly rotate the ‘I’ screw in counterclockwise direction until the chainsaw runs smoothly.
While the engine still runs, adjust the screw labeled ‘L.’ Slowly rotate the ‘L’ screw on clockwise until the chainsaw’s RPMs drop. Note the screw’s position. Now slowly rotate the ‘L’ screw on counterclockwise until the chainsaw’s RPM speeds up and then lowers again. Mark the screw’s position. Adjust the ‘L’ screw between these two marked positions.
Test the saw by making a cut on the piece of wood. Should the saw seem to lose its power through the test cut, or exhaust smoke, turn the screw labeled ‘H’ clockwise slightly and try making another cut. Keep on turning very slightly until the your Craftsmen Chainsaw can cut through the piece of wood smoothly without smoke.
Stihl Chainsaw Carburetor Rebuild
Before disassembling the carburetor, it is important to clean it by wiping it down using paper towels as well as blowing off loose dirt.
- Start by removing the plate covering the diaphragm and check if it is used well. Remove the gaskets and place them down in the order you disassembled them. Flip the carburetor over and take out the other cover after loosening the Philips head screw. A gasket and screen will be uncovered on this side. Also, lay them down in the order you disassembled them.
- Before replacing the gaskets, you may need to clean or replace the fuel screen and needle valve. At this stage, you need to be cautious as the components here are small and may fall and get lost. You will see a rocker held in place using a Philips head-screw. Put your thumb on the rocker’s side closest to the carburetor’s side. After loosening and removing the screw, slowly remove your thumb and collect the needle, screw, spring, and rocker arm. You may consider placing these tiny components on a magnetic surface.
- With every gasket remover, now you can clean the carburetor using a cleaner. Soak it and allow the cleaner to pass through every passage in the carburetor.
- After cleaning or replacing any component you needed to replace, you can start reassembling the carburetor. Start by putting back the screen. Now put back the needle valve by first returning the small spring back where it was. Put the needle back into the rocker’s arm. Put the rocker’s arm and the needle back into the carburetor. Again, press your thumb on the rocker’s side as place back the Philips screw.
- Moving to the gaskets, you basically just aline the holes and lay them back down by flipping them back. Do the same for the other side. Place back the gasket parts by flipping them back.
- Now the carburetor is fully reassembled. You can place it back on the chainsaw by first re-attaching the gas tube and throttle wire. The gas pipe is the longest of the two tubes and reconnects at the black barb. Once these two have been reattached, the carburetor can be placed on the threaded stud. The chrome barb lines up with and will self-attach to the impulse pipe. Now tighten the nuts.
- Lastly, you need to reconnect the throttle wire with the trigger. If none of the adjustment screws were turned during the rebuilding process, the carburetors should be good and working.
Hopefully this guide has been useful. Chainsaws can be tricky to fix and maintain, if you are finding it too hard, maybe its time for a change get started by looking at our chainsaw buying guide to make life easier.