Carburetor Adjustment On Pro Saws
All saws occasionally need to have their carburetor adjusted. A saw with a properly adjusted carburetor will produce maximum power, minimal smoke, run and idle smoothly, and give trouble free service. A saw that is too rich will produce excessive smoke and have insufficient power. A saw that is adjusted too lean will also have insufficient power, but this condition can quickly cause engine damage. The following information outlines the process of adjusting a carburetor on a pro saw.
Most Pro Saw Engines Have Three Carburetor Adjusting Screws:
- Idle Speed/Throttle Stop - This is the adjustment that controls how much the throttle valve (butterfly) stays open when the throttle trigger is released. If this adjustment is set too low, the engine will die when the throttle trigger is released. If this adjustment is set too high, the high idle speed will cause the centrifugal clutch to engage and the chain will run. This is a dangerous condition.
- Low Speed Fuel Adjustment - This is the adjustment that controls the proportion of fuel in the air/fuel mixture at idle speed. An adjustment that is too rich will cause the engine to load up and die at idle speed. A mixture that is too lean will starve the engine and cause it to race or surge. An extremely lean adjustment will cause the engine to die, too.
- High Speed Fuel Adjustment - This is the adjustment that controls the proportion of fuel in the air/fuel mixture at cutting speed. It would not be accurate to say this is the most important setting, because all of these adjustments need to be accurate for a saw to perform its best, but this is the adjustment that determines how the saw runs in the cut. An adjustment that is set too rich will not allow the saw to reach the RPM level necessary to build maximum power. Throttle response may also be sluggish and the engine will smoke and perform poorly. A mixture that is too lean will allow the engine to reach an RPM level where bearing failure and cylinder seizure are likely. It will also lack power in the cut and tend to run very hot.
Rich Running Conditions
An over rich carburetor adjustment is when the proportion of fuel in the air/fuel mixture is too high. When this occurs, the fuel does not burn well. What does burn, does not produce much heat, so the power stroke is weak. The partially burned mixture is expelled into the muffler and exits the saw as smoke. An over rich condition also causes carbon buildup.
Lean Running Conditions
A lean carburetor adjustment is when the proportion of fuel in the combustible air/fuel mixture is so low that there is not enough fuel to burn. This also makes a weak power stroke and causes the saw to have insufficient power. In addition to low power, a lean condition causes the cylinder temperature to rise, which can lead to a seizure. A lean condition also allows for excessive RPM, causing rod bearing failure.
It is best to use a digital tachometer when adjusting the carburetor on a pro saw. These tachs are easy to use and require no wires. When the tach is placed near the spark plug, it picks up an electrical signal when the plug fires. On a two-cycle engine, this occurs every engine rotation, so the tachometer simply counts the pulses and displays the results.
Carburetor Adjustment Procedure
- Before you start the saw, locate a small flat-bladed screwdriver. The screwdriver needs to be small enough to fit through any adjustment hole. Make sure the holes are free from debris and the ends of the adjustment screws are visible. On some saws, these areas can pack with chips, making adjustment difficult or impossible.
You're also going to need a tachometer. It is difficult (for even a trained ear) to adjust today's saws as accurately as is necessary without a tach. We have adjusted thousands of saws and we use a tachometer religiously.
- Begin by checking the saw's air filter. Clean it if necessary. Adjusting the carburetor with the air filter partially clogged is like adjusting the carburetor with the choke partially on. If you adjust your saw with a dirty air filter, the saw will run too lean when the filter is cleaned.
- Check the fuel level. The tank should be over half full. If the carburetor is adjusted when the fuel tank is nearly empty, the carburetor may be adjusted too rich when the fuel tank is filled.
- Start the engine and warm it up. Carburetor adjustments made on a cold engine will be too rich when it reaches normal operating temperature.
- Begin by setting the idle speed. Try to set the speed at about 2700 RPM. If you don't have a tachometer, try to set the speed so the saw will idle with the chain stopped. Never set the idle so the chain runs when the throttle is released. If the saw will not idle, go to the next step.
- Set the low speed fuel adjustment. Slowly turn in the screw until the engine surges or starves for fuel (lean). Make a mental note of the position of the screwdriver slot. Now slowly turn the adjustment screw out and the engine should run better. Keep turning the screw until the engine starts to load up (rich). Make a note of the position of the screwdriver slot and compare it to the position of the lean adjustment. Now slowly turn in the screw to a position where it idles the best. It should be about midway between the rich and lean positions.
Click on the link below and a WAV sound clip will be loaded into your browser. What you'll hear is an idling saw. Slowly we lean the low speed adjuster until the idle climbs and it then starts to die. Then we go rich and the engine starts to blubber, the RPM's drop, and the engine almost dies. The optimum setting is between these two extremes.
These are approximately. 25 seconds long, but require time to load. Those of you with slow systems or connections may not want to wait! Click here for Saw Idle Adjustment Sound WAV
- Go back to step (4) and reset the idle speed. Chances are that the RPM setting has changed since you optimized the fuel mixture adjustment.
- Set the high speed fuel adjustment. Hold the trigger wide open and check the RPM with the tachometer. The listing below identifies the maximum RPM setting for popular pro saws with bar & chain and no load:
- STIHL 044, MS440, 046, MS460 - 13,500 RPM
- STIHL 066, MS660 - 13,000 RPM
- STIHL 084, 088, MS880 - 11,500 RPM
- HUSQVARNA 272, 372 - 13,500 RPM
- HUSQVARNA 288, 385, 390, 394, 395 - 13,000 RPM
- HUSQVARNA 3120 - 11,500 RPM
- Click on the link below and a WAV sound clip will be loaded into your browser. What you'll hear this time is a saw being adjusted for full speed. After revving it up to max RPM and holding the trigger, we adjust the high speed rich, causing it to slow down and blubber. Then we adjust it lean, causing it to sound smoother, but then it starts to starve for fuel. As we back it off from lean to rich again, the sound becomes slightly rougher. This slightly rough sound (or 4-cycle sound, as it's sometimes referred to) is where you want it to be. We like to say, as "close" to the smooth as you can get it, but still just slightly into the rough.
This one is larger than the first, and requires more time to load. Those of you with slow systems or connections may not want to wait! Click here for Saw Full Rev Adjustment Sound WAV
- Go back to step (4) and fine tune the idle speed adjustment and low speed fuel adjustment. Movement of one adjusting screw often causes the other two to need readjustment.
- Your saw is properly adjusted and ready for work.
Why A Carburetor Has To Be Readjusted
If a carb is set right when a saw is new, why does it have to be readjusted? Some people wonder why their saw needs occasional tuning. They don't understand why saws can't be set at the factory and stay correctly adjusted for the life of the saw. The reason is there are many operational changes a user makes without realizing it. These changes include working at different elevations, changes in fuel, and a host of other factors cause saws to need periodic carburetor adjustment.
Today, sophisticated electronics can monitor and meter air/fuel needs. With this technology, saws will be able to "self adjust." This technology is well developed for automobiles and trucks. The process of miniaturizing an economical and durable system that will work on a saw engine is being developed. Until then, keep your tachometer and screwdriver handy.
The preceding information briefly explains rich and lean running conditions. It also identifies the three adjustment screws and their function. It should be noted that on today's pro saws, most of these adjustments have "limiters" that limit the range of carburetor adjustment. In most cases, proper adjustment is within this range, but not always. If proper adjustment for your saw is outside the limited range, take your saw into a shop. Sometimes this is caused by a problem with your saw, and sometimes the range on the limiters just needs to be reset.
Got questions or comments? Call or stop in.
How to Tune a Chainsaw Carburetor
In a recent blog I referenced the Game of Logging courses I attended and described all the new things I learned about safe and efficient use of a chainsaw. One such item was chainsaw maintenance, and one part of that was the carburetor test. I’ve run chainsaws for over 30 years and never knew to how adjust the carburetor. If you have a new saw, this won’t apply to you, as new regulations require saws to be built so that only a qualified technician can tune the carburetor. However, if you have an older saw, here’s how to quickly tune it yourself. Start by locating the three adjustment screws. They are typically labeled L (low speed jet), H (high speed jet), and I (idler jet). Your saw may be labeled differently (in the photos in the Gallery below, the idler jet is labeled “S”), but you’ll have three screws that correspond to these descriptions. Search your owner’s manual for guidance on how to adjust the carburetor.
Note: Your owner’s manual may advise you not to adjust the carburetor without a tachometer, which helps ensure you don’t run the engine too high. If you have a tachometer, great. If not, you can still follow the steps below to tune the carburetor, being careful not to rev the engine longer than suggested here.
Now, let’s tune your saw.
1. Start your saw and run it for a few minutes to warm it up.
2. Set your saw down, let it idle for 30 seconds, and then pick it up and tip it forward (handle up and bar down).
3. If it keeps running, go to Step 4. If it stalls, tighten the Low Speed screw. This will reduce the amount of fuel entering the carburetor. Repeat Step 2 as necessary.
4. Rev (accelerate) the idling saw.
5. If it accelerates fine, go to Step 6. If it “dogs,” loosen the Low Speed screw. This will increase the amount of fuel entering the carburetor. Repeat Step 4 as necessary.
6. Rev the idling saw for about 5 seconds (never rev it for 10 seconds or longer).
7. If it “flutters” while being revved, this is good, so go on to Step 8. If it “screams” while being revved, this is bad. Loosen the High Speed screw. Repeat Step 6 as necessary.
8. If the chain is stationary while the saw idles, you’re finished.
9. If the chain rotates around the bar while the saw is idling, adjust the Idler Screw as necessary to make it stop. This situation can be fixed in a matter of seconds and is extremely dangerous if not corrected.
That’s it. Less than five minutes of your time can make a big difference in how well your saw runs. Two additional tips are 1) use hot water and dish soap to clean a paper-type air filter (let it dry before using), and 2) use chainsaw gas to clean a wire-type air filter (you don’t need to let it dry before using).
This information will help your saw run more effectively and efficiently. This will allow your saw to last longer, and it will require less force and labor on your part. Collectively these equate to safer operating conditions and more seasons in the deer stand for you.
| By Kip Adams
How to Adjust a Chainsaw Carburetor Without a Bar & Chain
By Chris Deziel
It's best to adjust the carburetor of your chainsaw while the bar and chain are attached, because the sounds generated by the saw help you gauge the best settings. If you're in the middle of a thorough cleaning and maintenance procedure, however, you may want to make the adjustment before connecting the bar and chain. There's no reason why you shouldn't do this, but it's especially important to have a tachometer available to measure engine speed. A digital tachometer is easy to use; just place it next to the spark plug to get a reading.
Remove the air filter, and clean or replace it. If you make the adjustment with a dirty filter, the engine will run lean when you do get around to cleaning it.
Change the fuel if it's older than six months. Whether you change the fuel or not, fill the gas tank all the way. Making the adjustment on a half-empty tank could make the fuel mixture too rich the next time you fill the tank.
Start the saw and let it idle for 3 to 4 minutes to warm up. Locate the carburetor adjustment screws. They are usually near the air filter, and you should see three of them. They are usually marked "I," "L" and "H," for idle, low-speed and high-speed adjustments respectively.
Turn the idle screw clockwise with a flat-head screwdriver until the chain sprocket begins to spin. Back the screw off until the sprocket stops, then try to set it as far clockwise as you can without making the sprocket spin. The tachometer should read between 2,500 and 3,500 rpm.
Adjust the low-speed screw next. Turn it clockwise until the engine begins to run unusually fast and make a mental note of that position. Turn it the other way until the engine begins to run heavy and sputter, then turn it midway between these points.
Engage the throttle to make the high-speed adjustment. With the engine running at full speed, turn the high-speed screw clockwise until the engine starts to race. At this point, the fuel mixture is lean. Turn the screw the other way to allow more gas into the combustion chamber -- the sound of the engine should be fuller. Note this position.
Turn the screw counterclockwise until the engine begins stalling, then turn it back to the point at which the engine begins to run smoothly. It should be a little before the setting you noted previously. Check the engine speed with the tachometer. It shouldn't be any more than the highest recommended speed for your saw. For most saws, this is about 13,000 rpm.
Readjust the idle and low-speed screws after setting the high-speed screw.
- Adjusting the high-speed screw to deliver a mixture that is too lean can make the engine run too fast and burn it out. To avoid this, look up your saw's manual on the manufacturer's website and check the specification for maximum engine speed. Do not exceed this speed.
Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.
Carb Tuning for Dummies
Trying to simplify things a bit for carb tuning. I went from zero knowledge just a few months ago, to way too much knowledge at this point after reading all the posts on here regarding this subject. I mean if you read some of these tuning threads, it's a bit overwhelming. So, with my limited knowledge of tuning my 2 stroke equipment, saws, blowers, trimmers, etc., I wanted to check to see if I understand the concepts correctly, or if I need to adjust what I think I know and learn more. So here goes.
1. Begin with fresh fuel mix, clean air filter, check fuel filter, clean or new spark plug, clean muffler and spark arrestor.
2. Start with the L and H screws out from seat at about 1.5 turns for most 2 stoke carb applications.
3. Begin with idle, L, and LH or T or whatever opens the butterfly and adjust until idle is steady and continues to idle when turned every which way but loose. (Up, down, right, left, etc.) Then adjust the LH or T or whatever to keep the chain or clutch from spinning and continue to allow for proper idle. Turn it all around again to make sure it doesn't die. The L and LH together will allow for proper throttle response when the trigger is depressed. If there is lag or hiccup, then adjust the L leaner, clockwise toward seat until idle and throttle response is acquired.
4. End with turning the H to proper MAX rpm. Turn clockwise (right) to go faster (lean), turn counterclockwise (left) to go slower (rich).
If tuning by ear, then err on the slow side with H. Listen for the device to start to scream, then back it off until starts to have hard time keeping up, then put it somewhere in the middle.
If using a tach, as long as the desired idle rpm and max rpm are reached and the throttle responds well, is the saw pretty much tuned at this point? Is it possible with a tach to reach this effect (running great with the proper idle, response, and max rpm) with a saw or really any 2 stroke and run it lean, burn the piston if you stay below the MAX rpm for the saw or device? The only other thing I know to do is pop the spark plug after running a bit and see if it is dark and wet (rich), white (lean), or light tan (just right).
The reason I go through all this, I have a new TT-20K tach and it seems that I'm still dark and wet (rich), on a little Poulan from my testing this weekend. I can consistently rev to 12-12.5K and it still looks rich to me. Poulan gave me a MAX of 12K for the 2150. I've seen 12.6K as well for that model so I'm thinking the Poulan tech wanted me below by a bit for my own good. Rich is better than lean obviously, but wondering if I was off on any of my tuning methods. Started with my little $20.00 Poulan in case I blew it up. Now I need to move on to my Stihl's, so I want to make sure I'm on track with this method.
Also, when I pulled the plug on the 2150 Poulan, it was wet and dark (rich), but maybe it should be that way given that I only idled and revved the saw for a few seconds at a time while getting it to MAX rpm. Would it probably go more tan like it's supposed to if I were to actually get to run it in wood during normal course? Or, maybe while I was getting the settings right, it was rich and the plug didn't get enough time to clean itself when I did get the rpm's right. Much thanks for useful input.
Carb tuning chainsaw
A carburetor is an exceptional part of a chainsaw that controls the quantity of fuel used by the machine.
It is crucial to tune this section of the chainsaw properly because otherwise, your tool could malfunction and become difficult to use. A too costly adjustment could damage the engine eventually, which is why you need to be super careful with tuning.
Why Is Carburetor Important?
When it comes to a fuel chainsaw, a carburetor determines how little fuel will mix with air, which helps run the tool.
If too much fuel mixes with air, the engine will eventually get flooded with fuel. And too little fuel will leave chainsaw with less power, which means there will be smoke. As a result, there will be a build-up of carbon, which could damage the engine.
Three Adjusting Screws
Carburetors of most chainsaws come with three adjustments:
When the throttle trigger is released, this adjustment determines how much the throttle valve will remain open. Too high idle speed will cause saw’s centrifugal clutch to start working, and the chain will start running. On the other hand, too low idle speed will make your engine die as soon as the throttle trigger has been released.
This adjustment controls how much air and fuel will mix for cutting speed. A few people might argue that this is probably the most critical adjustment screw out of all three.
If this adjustment is too high, the saw will not reach a required RPM level needed for maximum power. Too low of modification will give you an RPM level where cylinder seizure and bearing failure could occur.
This adjustment determines how much air and fuel will mix during idle speed. Too less of an adjustment will make engine surge due to starvation. And too high of a change will cause the engine load up and eventually die. The engine could also die if the adjustment is extremely low.
How to Adjust a Carburetor?
- Take a look at the air filter and if required, clean it up. If you do not clear up any clogs that remained, you will end up adjusting the saw with a dirty filter. Eventually, when the filter is cleaned, the saw will end up running lean.
- After that, check the fuel level of the saw. Make sure that the tank is more than half full. If you adjust the chainsaw with low fuel, when you fill-up the tank eventually, the carburetor may become too adjusted. Then start the engine and let it warm since a cold engine might give you a rich adjustment.
- Then, you will need to focus on idle speed. Start by setting the speed at 2700 RPM, using a tachometer. Just make sure that the saw does not stay idle, making the chain run as soon as the throttle is released.
- For low-speed adjustment, turn screw inwards until the engine starves and note the position of the screw then. After that turn screw outwards to make the engine run better and then start to load up.
- Note this position of the screw as well. The optimum position of the screw should be somewhere between first and second noted positions, where the machine will idle best.
- For high-speed adjustment, turn screw inwards until the fuel mixture leans out. Then turn it inwards until you hear a flutter. You should now have a correct RPM, which you can check out with a tachometer.
- For further clarification, please check the chainsaw's manufacturer's website for additional instructions.
Tips for the Process
Make sure the machine is lying on a flat surface first. There should be no extra items around the saw, especially near the chain area. You do not want anything to snag on the chainsaw blades by mistake during the adjustment process.
It is a great idea to wear protective hand gear such as leather gloves. Also, have a set of safety goggles on, along with a full-sleeved shirt and long pants too.
Because the carburetor is a key piece to the chainsaw, it is a good idea to know how to adjust it. In this way, you could make sure that your machine has been running appropriately. As a result, your tool will last you a long time.
Some Other Chainsaw Related Articles:
- How does chainsaw function?
- Beginners’ guide to use a chainsaw avoiding risks
- How to measure sizes of your chainsaw chain?
How to Adjust a Chainsaw Carburetor
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. To find replacement Carburetors and other chainsaw parts CLICK HERE…
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.
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