The Importance of Fuel Air Adjustment Screws and Carburetor Adjustments

The engine is a complex system that requires precise adjustments to run smoothly. One of the key components that can affect how the engine runs is the fuel air adjustment screws. These screws are designed to fine-tune the airflow into the engine, ensuring that the fuel-to-air mixture is just right. However, there are many factors that can affect the performance of these screws and the overall health of the engine.

One of the reasons why we need to use fuel air adjustment screws is because of the condition of the air. The air filter and the fuel filter play a crucial role in ensuring that the engine receives clean air and fuel. If either of these filters is dirty or clogged, it can affect the performance of the engine. Similarly, if there are leaks in the system, such as a barrel gasket leak, it can draw in extra air into the engine, making it run too lean.

A slight leakage in the main seals can also cause problems for the engine. The job of the main seals is to keep pressure within the crank case, and if they are slightly damaged, it can let air into the engine. This can lead to a situation where the engine runs too lean, regardless of how much we adjust the carburetor settings.

In addition to these issues, the inlet manifold can also degrade over time, allowing air to enter the system when it shouldn't be there. This can also cause problems with the fuel-to-air mixture, leading to a lean mixture that can damage the engine.

One of the most significant benefits of using fuel air adjustment screws is that they allow us to fine-tune the carburetor settings to suit our specific needs. By making adjustments to the screws, we can ensure that the engine runs smoothly and efficiently, regardless of the conditions it is operating in.

However, if we add all these factors together - a slight blockage in the carburettor, fuel issues, an old or dirty air filter, running in a humid environment or cold weather followed by warm weather, and then switching to different fuels at high altitude - it becomes clear why we need to use these adjustment screws.

In reality, rather than being something that is wished upon us, repair specialists online has made the best of this development and created free printable downloads available on their website. From a downloadable guide for Briggs & Stratton diaphragm replacement to a comprehensive checklist for lawnmower ignition coil care, there are numerous resources available for those looking to improve their machine's performance.

The process of obtaining these free downloads is straightforward. To start, users can click on the "free printable downloads" button, which takes them to the download page where they can access six free downloadable guides. The best part? They're absolutely free, with no payment required whatsoever.

To get started, simply fill in your name and email address, and then click on the "get my download" button. You'll be able to view and download these valuable resources straight from your PC. The process is quick and easy, making it a great way to improve your machine's performance without breaking the bank.

Overall, fuel air adjustment screws are an essential component of any engine. By understanding how they work and making adjustments as needed, we can ensure that our machines run smoothly and efficiently. And with the help of resources like repair specialists online, it's easier than ever to get started on the path to improved performance.

"WEBVTTKind: captionsLanguage: encarburetor adjustment screws they're so complicated they're a pain why do we need them why can't we just have a carburetor and it works why do we need to keep trying to adjust a carburetor well this video is going to show you why we do need them and as usual I'm going to put in some visuals for a deeper understanding welcome to the repair specialist Channel I'm Craig the owner and Creator and having been in the trade for around 30 years I now make videos relating to the diagnosis and repair of small engines and machinery and how things work and why and in layman's terms using clear visual explanations to help you gain a deeper understanding and a firmer knowledge base why because knowledge is power so let's get to it and supporting this video is a free download leaflet of how to tune your chainsaw there's a link in the description below that will take you onto my website where you can download this as I've said completely free the best of it is is it's printable and you can take it into your workspace with you and tune your chainsaw at your leisure okay so as usual let's take a look inside this machine at the engine and carburetor although I'm showing a chainsaw here the principles are the same for other two-stroke machineries so as we know when the engine starts to move it draws in air through the induction tube of the carburetor and as it passes the main jet it draws out fuel hopefully at the right amount to allow for a good ratio between air and fuel for the engine to run optimal and so on most two-stroke carburetors we know we have these fuel adjustment screws which allows more or less fuel into the induction tube of the carburetor but the question is why aren't carburetors just set from the manufacturer at the right setting that allows fuel into the induction tube for the right air to fuel mixture so we don't have to make any adjustments what are the adjustment settings for anyway doesn't it make it more complicated having them and wouldn't it be much more simple if we just went with a manufacturer setting well the direct answer is yes of course it would be much more simple if we could have carburetors this way but one of the reasons we need to adjust the fuel in the carburettor is not literally down just to the fuel itself it's because of the air that enters the carburetor so let's say this carburetor is preset to only allow a certain amount of fuel down through the main jet into the induction tube we could now say that the amount of fuel allowed into the induction tube is constant the only issue is and this is something that most people don't realize is that the air that comes into the induction tube to draw out the fuel is anything but constant and I don't mean that in the respect that when the engine is running at a maximum it's drawing in a maximum amount of air at a maximum speed compared to when it's idling it's much less which of course is a variation as well but those varying speeds should bring out the right amount of fuel for the engine's needs at the time what instead I'm actually referring to is that there's other factors that affect the air to begin with such as temperature humidity and altitude but how exactly do they have an effect well let's take a look and we'll start with temperature if we could see the air molecules and the air molecules are made up of different gases would see that the air molecules themselves are vibrating with energy and it's the temperature of the air that depends on how much these molecules vibrate and it's their vibration level that depends on how close or how far these molecules exist from each other so in this instance let's say the air is moderately warm there's going to be a certain gap between each molecule because of their vibrations and that means in a certain area there's only going to be so many molecules because they've spread out slightly from each other in other words there's a certain density to this Air at a moderately warm temperature so then if the air temperature was to increase to being hot we'd see that the molecules are vibrating even more erratically and they've spread out from each other further so we can see that compared to the moderately warm which had a certain volume of these air molecules we've got much less air molecules now in that same given area and so it's much less dense so in basic terms how does that affect the air to fuel ratio inside the carburettor well let's work off a moderately warm temperature we can see with this example that the moderately warm air has a certain density that's correct to give a good air-to-fuel ratio for the engine so let's say then that this carburettor was designed to run in this moderately warm climate with this level of air density to allow this fuel to be of the right Constitution with the air for the engine to run correctly and then we take the same carburetor and we go and run it in a hot climate where the air coming into the carburetor is much hotter and less dense what we would find is that the air to fuel ratio is now different we've actually got less air molecules in there compared to the set amount of fuel coming out of the main jet and that means we've now got an air to fuel ratio that's rich with fuel because there's more fuel to air ratio now the level of air molecules coming into the engine would of course reduce the efficiency of the engine and slow the engine down anyway and that would bring out less fuel but it would still be an air-to-fuel mixture that's too rich for the engine so in this situation we could either keep the engine running in this most inefficient way or if we've got fuel adjuster screws we can screw them in slightly and reduce the amount of fuel coming out of the main jet making the fuel more lean therefore making the fuel a better ratio with the air that's available allowing the engine to run as best as it can which of course would be much better than it was if we didn't adjust it okay so let's have a look at what happens in a cold climate let's imagine then that we've got our moderately warm climate back a moderately warm air and because in this scenario our carburetor was set in a moderately warm climate let's now see what happens if we take this carburetor and we use it in a cold climate so if this carburetor has been set let's say in the spring or early summer and we don't use it again until the winter what's going to happen there well let's take a look at our air molecules again we can see with a moderate temperature they're vibrating at a certain speed allowing them a certain distance from each other but when the air gets cold their vibration drastically reduces and because of that they can aggregate closer together and that means in the given area that we've been talking about there's more air molecules therefore the air is more dense so inside our carburetor that's set for a moderately warm climate we can see now that the increased density of the air means that there's too much air in there now compared to the set amount of fuel and because we've now got far less fuel than air it's now a lean air to fuel mixture and the engine just won't run right and again we could either use the machine in this weakened state or if we've got fuel adjustment screws we can unscrew them slightly letting more fuel down into the induction tube and making it a better air to fuel ratio for the engine to run the best it can and on the other side of the coin then if this carburetor was set during the winter where we can see a good air to fuel ratio here now if this machine is then used in the Summer where the air is warmer we can see the problems we're going to get because the air is slightly warmer it's less dense and that's upset the air to fuel ratio once again it's become more rich so in this instance we can screw the adjuster screws inwards to reduce the amount of fuel coming out into the induction tube and making it a better air to fuel ratio once more okay so another factor that can affect air density is altitude and whilst it's unlikely that we're going to climb to the top of a very very large mountain and start using our Machinery certain differences in altitude can have an effect and that's because air or the gases that make up the air actually do have weight and as we know here on Earth anything with weight is affected by gravity and does gravity is basically the mass of the Earth pulling anything with weight to it there's no exception with air so that means that the Earth's gravity keeps most of the air molecules close to it so basically saying the closer we get to sea level the higher the concentration of air there will be and that's of course why human beings can get altitude sickness when they go to very high altitudes because the air there is less dense because they've evolved to need the density of air that's closer to sea level so now already we've got more factors that can affect carburetor settings we've got the temperature and now we've got the altitude on top of the temperature but if we just talk about altitude at the moment to keep it more simple then we can add these things together afterwards so then let's say we set this carburetor close to sea level and we've got a good air to fuel mixture because we've got a certain density of air coming in through the carburetor bringing out the fuel and we've matched it by the right amount of fuel by adjusting the fuel adjustment screws again I'm not exactly saying that we're going to take our Machinery to the top of a huge mountain and run it there but if we do take it to a higher altitude than what it's set for then it's likely we will experience some difference in the quality of its performance and that's because the air being drawn into the carburetor is much less dense than the air was when the carburetor fuel adjustment screws were set to allow the right amount of fuel out of the main jet at the higher air density nearer to sea level and so we've now gone from a good air-to-fuel ratio to having less air available and because of that we now have a rich air-to-fuel ratio we have too much fuel going in there then we have air to deal with it again this is going to affect the engine's performance so to get the engine work as best as we possibly can then what we need to do is to screw the adjustment screws in leaning out the fuel to make the fuel to air mixture a better ratio I'm not saying the engine is going to be at Peak Performance even when we've adjusted it because at the end of the day we have still got less air going into the engine but it will be better than leaving it with less air and too rich but adjusting it so that we can give it the right amount of fuel for the amount of air means that the engine can combust the ratio of air to fuel much better let's now come back down to near sea level I think we know what's going to happen now well because of our settings we have a lean amount of fuel available at the main jet and because now the air is much more dense we in effect have too much air to deal with this fuel or not enough fuel to deal with the large amount of air and so we now have a lean mix and the engine will not run right that's the basics on altitude so now what about humidity well let's come back to our Baseline good air to fuel mix and at the moment we've got a good supply of air coming into the carburetor making this decent air to fuel ratio but of course what happens in a humid environment is that water vapor is present in the air and so depending on the concentration of this water vapor at any given time then this vapor is going to take up space within the air and so when the engine draws in a specific volume into the carburetor it won't just be air molecules this water vapor will have displaced some of the air molecules and so there'll be less quality air going into the carburetor and into the engine and so now looking at the air to fuel mix we can see that we have less air to fuel ratio now and so principally now the ratio would be rich rich in fuel because we've got more fuel to air available to deal with it and so the best thing to do now is to screw in the screws slightly to restrict some of the fuel coming out of the main jet and make it a better air to fuel mix for combustion I'm not saying that the engine would run great because we do have water vapor going into the engine but in my opinion it would run better than water vapor going into the engine like this and it being too rich so by adjusting the carburetor as we've shown on all of these examples it's just to get the engine running as best it can I'm not saying it's going to perform at its best okay so other than air condition let's move on to other reasons why we need fuel adjustment screws and one particular thing I've most certainly come across in the past is the condition of the air filter let's say we've got a brand new air filter on this machine and that's letting a certain volume of air through into the carburetor and that volume of air is pulling out a certain amount of fuel out of the main jet in the Venturi of the carburetor and let's imagine that that's the right fuel to air mix to let this engine run correctly if the air filter was blocked then we'd know about it and the engine wouldn't run right at all and we'd have to change the air filter but when the air filter has some partial blockages it won't let the same volume of air through and because it isn't letting that original volume of air through then it's going to start running slightly richer and of course it will need the screws screwing slightly inwards to restrict some of that fuel to make it a better air to fuel mix again if it's totally blocked and needs a new filter it needs a new filter but before it gets to that stage of needing a new filter it is sometimes best just to slightly adjust the fuel screws in this way so what happens when we've adjusted our carburetor to suit this partially blocked air filter and then we put a new air filter on yep it's going to run lean because now it's allowing a high volume of air through and because we restricted the fuel with the fuel screws when we had the partially blocked air filter we're now running in that lean state so we can turn the field screws outwards and let more fuel down until we've got a better air to fuel mix allowing the engine to run better it's always best as well to check the fuel filter and make sure there's a new one on quite regularly because any restriction in fuel going up through the carburetor into the Venturi means that we're not going to get the right air to fuel mix and just like the air filter of course the fuel filter also collects crud and dirt that's its job and in time the fuel flow going into the carburettor does naturally reduce and just as this is starting to happen before it gets too blocked we can actually adjust the carburetor and make things run a little better and let's not forget blockages within the carburetor as well there's a screen filter in there just as that's starting to get blocked and starting to reduce the amount of fuel flow through the carburetor then we're gonna need to open up the fuel screws a little bit to try and bring more fuel into the induction tube of course until it gets too blocked and then we can't adjust it we need to clean the carburettor and there's lots of little fuel veins inside the carburetor as we already know that when they start to block up then we're going to start needing to adjust these screws to prevent the engine from running lean and then if we've made adjustments because of partial blockages and then we've cleaned the carburetor then we're going to get the carburetor running rich so we'll need to readjust it again another reason for adjustment is the fuels condition itself what we tend to find is as the fuel starts to age and starts to become more stale the reactive material that combust starts to evaporate into the environment and so it leaves behind a less reactive a less combustible fluid if you like I'm not suggesting that you use stale fuel but just at that stage as the fuel starts to become past its best I have found it beneficial to adjust the fuel screws on the carb slightly to find that sweet point of how the engine runs at its best under these conditions and then of course we've got the issue of different types of two-stroke oil inside the fuel and different concentrations of oil so really it's quite vast when we look at it in this way so one of the best things I've found is that just to try a fuel basically as long as it's good fuel and it's good oil put it into the machine see how the machine runs and then from that point we can see if it's running too rich we can adjust the fuel screws inwards to lean out the fuel and if it sounds like it's running too lean then we can unscrew the screws and richen up the fuel going into the engine there are so many different variables when it comes to how an engine will run and so many different things already what we've seen that can affect how that engine runs this is the reason why we need these fuel air adjustment screws and so far we've only looked at the condition of the air the fuel the oil the air filter and the fuel filter but sometimes it can be an issue where the carburetor or the engine is drawing in too much air from a different place other than the induction tube and it's this that can mess around with that otherwise good fuel to air ratio that gives us the need to adjust the carburetor for instance if there was leaks in important areas such as these then it can have dramatic effects on the engine for instance if there was an air leak through the barrel gasket then as the engine runs it would draw in extra air between the barrel and the crankcase and allow more air into the engine as we know by now any extra air can mess up that fuel to air mixture and make it too lean and of course if the leakage here was really bad then the engine wouldn't run at all properly no matter how much we adjust the carburetor but if there's just some slight leakage there if it's just started to leak and it's in its very early stages then this can be another reason as to why the engine's running slightly lean and of course then it's probably possible to adjust the carburetor to get the engine to run right for a while before the leak gets too bad and it's very similar with the main seals as the engine runs the job of the main seals is to keep pressure within the crank case and if the main seals are slightly damaged and letting air into the engine then again we're going to get a situation where the engine's running too lean and if these seals are truly damaged then no matter what we do with the carburettor settings we won't get this engine to run right but in the early days when the leak is only just started to form and it's a very small leak then we can adjust the carburetor to make it sound much better again until the problem takes hold and very similarly the inlet manifold can sometimes degrade and that can let in air where it shouldn't do and again that can lean up the field to air mixture if it's too badly damaged then no we're not going to get this engine to run right but if it's slightly damaged we're letting a slight amount of air through more than it should do then we can make carburetor adjustments until it gets too bad now if we was to start to add all of these things together we've got a slight amount of blockage in the carburettor the fuel isn't quite right the air filter isn't as good as it used to be we're in a humid environment or we're in a cold environment and then we move to a warm environment and then we put some good fuel in there but we now are to higher altitude then you can see why we need to use fuel adjustment screws so rather than the adjustment screws being something we wish we'd never seen we wish we'd never had on our carburetors we can start to see them now that they're there for our own benefit to help us make our machines run as best as they possibly can under the conditions that they have to run in okay so don't forget to take advantage of the repair specialistonline.com website where from the landing page you can click this button here free printable downloads onto the download page and you can see I've got six free downloads here the best of them are that they're printable and you can take them into your workspace with you and they're on several different topics we have one on lawnmower ignition coil care a checklist the Briggs and Stratton diaphragm replacement guide on flood your chainsaw without or with tools how to order the correct chain every time for your chainsaw how to tune a chainsaw guide and a chainsaw won't run as I've said they're absolutely free and the download buttons are in the gold and if I just take you through the process because I've been asked this question how you do this so click free download scroll down add to cart then view cart then get my download you can see here it's absolutely free there's no payment at all so get my free download for the phone number you may just use any number I don't need the phone number but we do need an email address okay so I've filled that in my name last name and email address and click and as you can see we're still here I have no charge and place order and then we come to this screen here thank you and your name and then it says download click download and off it goes onto your PC so a really big thank you for coming to the end of this video and I hope you've gained something from it thank you for watchingcarburetor adjustment screws they're so complicated they're a pain why do we need them why can't we just have a carburetor and it works why do we need to keep trying to adjust a carburetor well this video is going to show you why we do need them and as usual I'm going to put in some visuals for a deeper understanding welcome to the repair specialist Channel I'm Craig the owner and Creator and having been in the trade for around 30 years I now make videos relating to the diagnosis and repair of small engines and machinery and how things work and why and in layman's terms using clear visual explanations to help you gain a deeper understanding and a firmer knowledge base why because knowledge is power so let's get to it and supporting this video is a free download leaflet of how to tune your chainsaw there's a link in the description below that will take you onto my website where you can download this as I've said completely free the best of it is is it's printable and you can take it into your workspace with you and tune your chainsaw at your leisure okay so as usual let's take a look inside this machine at the engine and carburetor although I'm showing a chainsaw here the principles are the same for other two-stroke machineries so as we know when the engine starts to move it draws in air through the induction tube of the carburetor and as it passes the main jet it draws out fuel hopefully at the right amount to allow for a good ratio between air and fuel for the engine to run optimal and so on most two-stroke carburetors we know we have these fuel adjustment screws which allows more or less fuel into the induction tube of the carburetor but the question is why aren't carburetors just set from the manufacturer at the right setting that allows fuel into the induction tube for the right air to fuel mixture so we don't have to make any adjustments what are the adjustment settings for anyway doesn't it make it more complicated having them and wouldn't it be much more simple if we just went with a manufacturer setting well the direct answer is yes of course it would be much more simple if we could have carburetors this way but one of the reasons we need to adjust the fuel in the carburettor is not literally down just to the fuel itself it's because of the air that enters the carburetor so let's say this carburetor is preset to only allow a certain amount of fuel down through the main jet into the induction tube we could now say that the amount of fuel allowed into the induction tube is constant the only issue is and this is something that most people don't realize is that the air that comes into the induction tube to draw out the fuel is anything but constant and I don't mean that in the respect that when the engine is running at a maximum it's drawing in a maximum amount of air at a maximum speed compared to when it's idling it's much less which of course is a variation as well but those varying speeds should bring out the right amount of fuel for the engine's needs at the time what instead I'm actually referring to is that there's other factors that affect the air to begin with such as temperature humidity and altitude but how exactly do they have an effect well let's take a look and we'll start with temperature if we could see the air molecules and the air molecules are made up of different gases would see that the air molecules themselves are vibrating with energy and it's the temperature of the air that depends on how much these molecules vibrate and it's their vibration level that depends on how close or how far these molecules exist from each other so in this instance let's say the air is moderately warm there's going to be a certain gap between each molecule because of their vibrations and that means in a certain area there's only going to be so many molecules because they've spread out slightly from each other in other words there's a certain density to this Air at a moderately warm temperature so then if the air temperature was to increase to being hot we'd see that the molecules are vibrating even more erratically and they've spread out from each other further so we can see that compared to the moderately warm which had a certain volume of these air molecules we've got much less air molecules now in that same given area and so it's much less dense so in basic terms how does that affect the air to fuel ratio inside the carburettor well let's work off a moderately warm temperature we can see with this example that the moderately warm air has a certain density that's correct to give a good air-to-fuel ratio for the engine so let's say then that this carburettor was designed to run in this moderately warm climate with this level of air density to allow this fuel to be of the right Constitution with the air for the engine to run correctly and then we take the same carburetor and we go and run it in a hot climate where the air coming into the carburetor is much hotter and less dense what we would find is that the air to fuel ratio is now different we've actually got less air molecules in there compared to the set amount of fuel coming out of the main jet and that means we've now got an air to fuel ratio that's rich with fuel because there's more fuel to air ratio now the level of air molecules coming into the engine would of course reduce the efficiency of the engine and slow the engine down anyway and that would bring out less fuel but it would still be an air-to-fuel mixture that's too rich for the engine so in this situation we could either keep the engine running in this most inefficient way or if we've got fuel adjuster screws we can screw them in slightly and reduce the amount of fuel coming out of the main jet making the fuel more lean therefore making the fuel a better ratio with the air that's available allowing the engine to run as best as it can which of course would be much better than it was if we didn't adjust it okay so let's have a look at what happens in a cold climate let's imagine then that we've got our moderately warm climate back a moderately warm air and because in this scenario our carburetor was set in a moderately warm climate let's now see what happens if we take this carburetor and we use it in a cold climate so if this carburetor has been set let's say in the spring or early summer and we don't use it again until the winter what's going to happen there well let's take a look at our air molecules again we can see with a moderate temperature they're vibrating at a certain speed allowing them a certain distance from each other but when the air gets cold their vibration drastically reduces and because of that they can aggregate closer together and that means in the given area that we've been talking about there's more air molecules therefore the air is more dense so inside our carburetor that's set for a moderately warm climate we can see now that the increased density of the air means that there's too much air in there now compared to the set amount of fuel and because we've now got far less fuel than air it's now a lean air to fuel mixture and the engine just won't run right and again we could either use the machine in this weakened state or if we've got fuel adjustment screws we can unscrew them slightly letting more fuel down into the induction tube and making it a better air to fuel ratio for the engine to run the best it can and on the other side of the coin then if this carburetor was set during the winter where we can see a good air to fuel ratio here now if this machine is then used in the Summer where the air is warmer we can see the problems we're going to get because the air is slightly warmer it's less dense and that's upset the air to fuel ratio once again it's become more rich so in this instance we can screw the adjuster screws inwards to reduce the amount of fuel coming out into the induction tube and making it a better air to fuel ratio once more okay so another factor that can affect air density is altitude and whilst it's unlikely that we're going to climb to the top of a very very large mountain and start using our Machinery certain differences in altitude can have an effect and that's because air or the gases that make up the air actually do have weight and as we know here on Earth anything with weight is affected by gravity and does gravity is basically the mass of the Earth pulling anything with weight to it there's no exception with air so that means that the Earth's gravity keeps most of the air molecules close to it so basically saying the closer we get to sea level the higher the concentration of air there will be and that's of course why human beings can get altitude sickness when they go to very high altitudes because the air there is less dense because they've evolved to need the density of air that's closer to sea level so now already we've got more factors that can affect carburetor settings we've got the temperature and now we've got the altitude on top of the temperature but if we just talk about altitude at the moment to keep it more simple then we can add these things together afterwards so then let's say we set this carburetor close to sea level and we've got a good air to fuel mixture because we've got a certain density of air coming in through the carburetor bringing out the fuel and we've matched it by the right amount of fuel by adjusting the fuel adjustment screws again I'm not exactly saying that we're going to take our Machinery to the top of a huge mountain and run it there but if we do take it to a higher altitude than what it's set for then it's likely we will experience some difference in the quality of its performance and that's because the air being drawn into the carburetor is much less dense than the air was when the carburetor fuel adjustment screws were set to allow the right amount of fuel out of the main jet at the higher air density nearer to sea level and so we've now gone from a good air-to-fuel ratio to having less air available and because of that we now have a rich air-to-fuel ratio we have too much fuel going in there then we have air to deal with it again this is going to affect the engine's performance so to get the engine work as best as we possibly can then what we need to do is to screw the adjustment screws in leaning out the fuel to make the fuel to air mixture a better ratio I'm not saying the engine is going to be at Peak Performance even when we've adjusted it because at the end of the day we have still got less air going into the engine but it will be better than leaving it with less air and too rich but adjusting it so that we can give it the right amount of fuel for the amount of air means that the engine can combust the ratio of air to fuel much better let's now come back down to near sea level I think we know what's going to happen now well because of our settings we have a lean amount of fuel available at the main jet and because now the air is much more dense we in effect have too much air to deal with this fuel or not enough fuel to deal with the large amount of air and so we now have a lean mix and the engine will not run right that's the basics on altitude so now what about humidity well let's come back to our Baseline good air to fuel mix and at the moment we've got a good supply of air coming into the carburetor making this decent air to fuel ratio but of course what happens in a humid environment is that water vapor is present in the air and so depending on the concentration of this water vapor at any given time then this vapor is going to take up space within the air and so when the engine draws in a specific volume into the carburetor it won't just be air molecules this water vapor will have displaced some of the air molecules and so there'll be less quality air going into the carburetor and into the engine and so now looking at the air to fuel mix we can see that we have less air to fuel ratio now and so principally now the ratio would be rich rich in fuel because we've got more fuel to air available to deal with it and so the best thing to do now is to screw in the screws slightly to restrict some of the fuel coming out of the main jet and make it a better air to fuel mix for combustion I'm not saying that the engine would run great because we do have water vapor going into the engine but in my opinion it would run better than water vapor going into the engine like this and it being too rich so by adjusting the carburetor as we've shown on all of these examples it's just to get the engine running as best it can I'm not saying it's going to perform at its best okay so other than air condition let's move on to other reasons why we need fuel adjustment screws and one particular thing I've most certainly come across in the past is the condition of the air filter let's say we've got a brand new air filter on this machine and that's letting a certain volume of air through into the carburetor and that volume of air is pulling out a certain amount of fuel out of the main jet in the Venturi of the carburetor and let's imagine that that's the right fuel to air mix to let this engine run correctly if the air filter was blocked then we'd know about it and the engine wouldn't run right at all and we'd have to change the air filter but when the air filter has some partial blockages it won't let the same volume of air through and because it isn't letting that original volume of air through then it's going to start running slightly richer and of course it will need the screws screwing slightly inwards to restrict some of that fuel to make it a better air to fuel mix again if it's totally blocked and needs a new filter it needs a new filter but before it gets to that stage of needing a new filter it is sometimes best just to slightly adjust the fuel screws in this way so what happens when we've adjusted our carburetor to suit this partially blocked air filter and then we put a new air filter on yep it's going to run lean because now it's allowing a high volume of air through and because we restricted the fuel with the fuel screws when we had the partially blocked air filter we're now running in that lean state so we can turn the field screws outwards and let more fuel down until we've got a better air to fuel mix allowing the engine to run better it's always best as well to check the fuel filter and make sure there's a new one on quite regularly because any restriction in fuel going up through the carburetor into the Venturi means that we're not going to get the right air to fuel mix and just like the air filter of course the fuel filter also collects crud and dirt that's its job and in time the fuel flow going into the carburettor does naturally reduce and just as this is starting to happen before it gets too blocked we can actually adjust the carburetor and make things run a little better and let's not forget blockages within the carburetor as well there's a screen filter in there just as that's starting to get blocked and starting to reduce the amount of fuel flow through the carburetor then we're gonna need to open up the fuel screws a little bit to try and bring more fuel into the induction tube of course until it gets too blocked and then we can't adjust it we need to clean the carburettor and there's lots of little fuel veins inside the carburetor as we already know that when they start to block up then we're going to start needing to adjust these screws to prevent the engine from running lean and then if we've made adjustments because of partial blockages and then we've cleaned the carburetor then we're going to get the carburetor running rich so we'll need to readjust it again another reason for adjustment is the fuels condition itself what we tend to find is as the fuel starts to age and starts to become more stale the reactive material that combust starts to evaporate into the environment and so it leaves behind a less reactive a less combustible fluid if you like I'm not suggesting that you use stale fuel but just at that stage as the fuel starts to become past its best I have found it beneficial to adjust the fuel screws on the carb slightly to find that sweet point of how the engine runs at its best under these conditions and then of course we've got the issue of different types of two-stroke oil inside the fuel and different concentrations of oil so really it's quite vast when we look at it in this way so one of the best things I've found is that just to try a fuel basically as long as it's good fuel and it's good oil put it into the machine see how the machine runs and then from that point we can see if it's running too rich we can adjust the fuel screws inwards to lean out the fuel and if it sounds like it's running too lean then we can unscrew the screws and richen up the fuel going into the engine there are so many different variables when it comes to how an engine will run and so many different things already what we've seen that can affect how that engine runs this is the reason why we need these fuel air adjustment screws and so far we've only looked at the condition of the air the fuel the oil the air filter and the fuel filter but sometimes it can be an issue where the carburetor or the engine is drawing in too much air from a different place other than the induction tube and it's this that can mess around with that otherwise good fuel to air ratio that gives us the need to adjust the carburetor for instance if there was leaks in important areas such as these then it can have dramatic effects on the engine for instance if there was an air leak through the barrel gasket then as the engine runs it would draw in extra air between the barrel and the crankcase and allow more air into the engine as we know by now any extra air can mess up that fuel to air mixture and make it too lean and of course if the leakage here was really bad then the engine wouldn't run at all properly no matter how much we adjust the carburetor but if there's just some slight leakage there if it's just started to leak and it's in its very early stages then this can be another reason as to why the engine's running slightly lean and of course then it's probably possible to adjust the carburetor to get the engine to run right for a while before the leak gets too bad and it's very similar with the main seals as the engine runs the job of the main seals is to keep pressure within the crank case and if the main seals are slightly damaged and letting air into the engine then again we're going to get a situation where the engine's running too lean and if these seals are truly damaged then no matter what we do with the carburettor settings we won't get this engine to run right but in the early days when the leak is only just started to form and it's a very small leak then we can adjust the carburetor to make it sound much better again until the problem takes hold and very similarly the inlet manifold can sometimes degrade and that can let in air where it shouldn't do and again that can lean up the field to air mixture if it's too badly damaged then no we're not going to get this engine to run right but if it's slightly damaged we're letting a slight amount of air through more than it should do then we can make carburetor adjustments until it gets too bad now if we was to start to add all of these things together we've got a slight amount of blockage in the carburettor the fuel isn't quite right the air filter isn't as good as it used to be we're in a humid environment or we're in a cold environment and then we move to a warm environment and then we put some good fuel in there but we now are to higher altitude then you can see why we need to use fuel adjustment screws so rather than the adjustment screws being something we wish we'd never seen we wish we'd never had on our carburetors we can start to see them now that they're there for our own benefit to help us make our machines run as best as they possibly can under the conditions that they have to run in okay so don't forget to take advantage of the repair specialistonline.com website where from the landing page you can click this button here free printable downloads onto the download page and you can see I've got six free downloads here the best of them are that they're printable and you can take them into your workspace with you and they're on several different topics we have one on lawnmower ignition coil care a checklist the Briggs and Stratton diaphragm replacement guide on flood your chainsaw without or with tools how to order the correct chain every time for your chainsaw how to tune a chainsaw guide and a chainsaw won't run as I've said they're absolutely free and the download buttons are in the gold and if I just take you through the process because I've been asked this question how you do this so click free download scroll down add to cart then view cart then get my download you can see here it's absolutely free there's no payment at all so get my free download for the phone number you may just use any number I don't need the phone number but we do need an email address okay so I've filled that in my name last name and email address and click and as you can see we're still here I have no charge and place order and then we come to this screen here thank you and your name and then it says download click download and off it goes onto your PC so a really big thank you for coming to the end of this video and I hope you've gained something from it thank you for watching\n"