An ATV carburetor performs the vital role of mixing air and gasoline (in the right amounts) before getting the mixture into the ATV’S cylinders. Although not commonly used in modern ATV releases, carburetors are still popular for owners who don’t mind tuning their cars or ATVs frequently. But how does an ATV carburetor work?
An ATV carburetor works by mixing air and fuel to allow for internal combustion. Carburetors usually have a narrow kink called a venturi that speeds up the air, thus lowering its pressure. Decreased air pressure allows the fuel pipe to release fuel, allowing air and fuel to mix in the cylinders.
Curious to learn how an ATV carburetor works? Then you couldn’t be in a better place. Read on as we break down the basic functions of a carburetor.
A carburetor is a mechanical device that mixes fuel and air to allow for internal combustion. Its function is inspired by Bernoulli’s principle, which states that as air moves faster, its static pressure reduces, consequently increasing its dynamic pressure.
An ATV carburetor has an open pipe in the form of a venturi, which allows for the passage of air into the engine’s inlet manifold. The inlet manifold, also called the intake manifold, is part of the engine that supplies the air/fuel mixture to the cylinders.
The venturi widens and narrows strategically to regulate airspeed. You’ll find a butterfly valve known as the throttle valve, which can be turned to either block or allow airflow into the system. By controlling the amount of air that flows through the carburetor’s throat, the valve determines the air/fuel mixture ratio, thus regulating engine speed and power.
The narrowest part of the venturi usually has small holes that allow for the introduction of fuel. The presence of jets ensures that fuel flow is regulated precisely in the fuel path, thus allowing for proper combustion.
Carburetors usually vary in terms of design and complexity. However, most of these mechanical devices function on the same basic principle- mixing air and fuel to promote combustion and consequently power the engine.
You’ll find that most ATV carburetors use a simple design. They have a vertical air pipe that’s strategically located above the engine cylinders. The vertical air pipe is then joined to a horizontal fuel pipe (at the narrowest part of the venturi).
The failing pressure of the speeded-up air creates a much-needed sucking effect for the release of fuel. The air-fuel mixture can then be regulated through two swiveling valves located above and below the carburetor’s venturi.
The top valve is called a choke and regulates the amount of air that can flow in the venturi. When the choke is closed, airflow is restricted, allowing the venturi to suck in more fuel, thus giving the engine a fuel-rich mixture.
This comes in extra handy when the engine is cold, running quite slow, or when it’s just starting up.
The second valve is called the throttle and also helps to regulate the air-fuel mixture. The more the carburetor’s throttle is open, the more the airflow inside the carburetor, which translates to more fuel being sucked.
This results in more energy release, increased power, and eventually a faster ATV, hence explaining why opening the throttle valve allows an engine to accelerate.
Here’s a quick animation showing how a carb works:
Here’s a quick summary of how the ATV carburetor works:
Carburetors have been gradually phased out over the years, with more preference given to fuel injection systems. While both systems perform similar functions, carburetors are a lot hard to program, which decreases fuel economy and overall efficiency.
On the other hand, fuel injection systems are preferred due to their ability to deliver fuel straight to the cylinder. Carburetors tend to struggle when it comes to idling, which is pretty straightforward for the more modern fuel injectors.
Idling is possible with fuel injection since the system can gradually add small amounts of fuel to keep an engine going. Contrastingly, carburetors tend to have the throttle closed when idle. As a result, a carbureted engine will need an idle jet to prevent stalling after the throttle is closed.
Fuel injection systems also produce reduced levels of gas vapor, which reduces the chances of fire outbreaks.
Fuel injection systems have played a major role in the gradual phasing out of carburetors. A fuel injection system comprises a complex set of sensors and electronics, which allows for clean and highly efficient combustion.
ATV can either use carburetors or fuel injection systems to power the engine. Despite being phased out slowly, Carburetors have a simple working mechanism that makes them ideal for some ATV enthusiasts.
When the ATV engine is started, the choke (top valve) regulates the airflow into the pipe. The venturi plays a pivotal role in regulating air pressure inside the pipe, which determines the amount of fuel released from the tank.
The throttle also helps regulate the air-fuel mixture, allowing the engine to produce the power needed to accelerate the ATV.
Sharing is caring!
Last updated:
ATV Carburetor Adjustment involves tuning your ATV’s carb for maximum performance.
How do I know my jetting is off? My ATV bogs down a lot, is jetting to blame? I have performance parts, what now? These are all common questions so lets get you up to speed on ATV carburetor adjustment.
You can tune your own ATV jets and avoid common jetting mistakes if you understand some jetting basics, explained below. A comprehensive installation guide will come with the jetting kit you purchase for your make and model of ATV so instead this guide will focus on explaining the basic principles of how ATV jets work. How jetting works…
#1 – The first thing you need to remember is that ATV jetting refers to throttle position, not engine rpm. Each jet is effective for a specific throttle position range. The pilot jet, or pilot screw as it is sometimes referred to, controls the flow of fuel between Idle speed and about one eight of wide open throttle (WOT). The needle jet controls the flow of fuel from the one eight position up to about the three quarter throttle position.
Lastly your main jet controls the flow of fuel between the three quarter and wide open throttle positions.
#2 – The second thing you need to know is that aftermarket performance parts will change your jetting requirements. Increased engine performance usually means an increased demand for fuel so learning ATV carburetor adjustment techniques is important.
Other factors that affect jetting are rev limiters, altitude and fouled plugs if your jetting is off. Altitude directly affects engine performance because the higher you go from sea level the thinner the air gets.
The pilot jet, also referred to as pilot screw, controls carburetor fuel/air mixture between Idle and 1/4 throttle. Turning the screw IN makes the fuel/air mixture leaner. Turning the screw OUT makes the fuel/air mixture richer. Lean means less gas, rich means more gas.
Every jet is identified by a number and that number relates directly to the size of the opening inside the jet.
Again smaller is leaner, larger is richer. When jetting your carb if you find that you need to turn the pilot jet all the way in to improve response then you likely need to switch to a smaller number of screw.
If on the other hand you need to turn it more than 2.5 turns out you likely need a larger numbered screw. When your engine bogs down at the smallest increase in throttle position your pilot jetting is likely too rich.
The needle jet and its needle controls the fuel/air mixture from the 1/8th throttle position all the way up to the 3/4 throttle position. The needle within the needle jet is a long tapered pin. As you increase the throttle position the pin pulls out of its jet allowing the fuel/air mixture to become richer. There are several different shapes and diameter of needles/needle jets but the needle jet is often left alone during tuning as it doesn’t affect idle or top end performance. The same rich/lean characteristics apply as with the pilot screw.
The main jet controls the fuel/air mixture from 3/4 throttle position up to wide open throttle. Again the main jet is numbered and a larger number indicates a larger hole and a richer mixture. A stock engine will perform well with a stock main jet but once engine performance parts are added its likely that you will need to revisit at least the main jet of your carburetor. Different performance part combinations will create different demands from your carburetor. Anything that increases horsepower will also increase fuel demand.
All the performance parts in the world won’t improve performance if you don’t tune your carb. If you have a rev limiter in place you may need to tune or upgrade that as well because a rev limiter will tend to bog down the engine at full throttle. Make sure to follow the instructions included with most jetting kits.
Now that you, hopefully, understand a bit more about the basics of how ATV carburetor parts work these are the steps to take if you’re in a jam on the trails.
Blockage, damage, fuel contamination, mud in the air intake system and other conditions can cause your ATV carburetor to be unable to deliver the right amount of fuel to your ATV engine. You always want to tune your ATV carburetor at home or in the shop but that’s not always possible. If you’re in a jam, this is what you can do.
This is not attaching the carburetor to the engine, it’s going to turn freely if you adjust it.
You can continue to adjust it a bit until the engine sounds better and runs without hesitation. If you turn it too much you will eventually flood the engine with too much fuel and this will make it bog down and be hard to start as well. A flooded condition will require time for the fuel to evaporate.
Carburetor jets control the amount of fuel which is mixed with air inside the throttle body of your carburetor. This carburetor jet size chart shows you how effective each jet is at specific throttle levels. A Pilot jet is effective at idle speed up to 1/4 throttle(low-range). A needle jet is effective from 1/4 throttle to 3/4 throttle(mid-range). A main jet is effective from 3/4 throttle up to wide open throttle(top-end).
See also
When diagnosing a carburetor or tuning problem look at the jet responsible for the range in which the problem is occurring.
ALWAYS follow the manufacturer’s specifications whenever possible. Jet size is usually stamped onto the jet itself, typically in milimeters(mm), ranging from small to large. Changing a carb jet for a smaller sized jet will reduce fuel flow. Likewise, installing a larger jet will increase fuel flow and may help a performance engine run more smoothly. Note: an engine that runs rich is less likely to sustain heat damage than and engine that runs lean.
I hope that this carburetor tuning guide helps you understand how jets work so that you can best dial in your ATV for maximum performance(and fun!).
Note: compressed air is extremely helpful in clearing obstructions.Carburetor jets become clogged naturally over time and a periodic carburetor cleaning is required. Always consult with your ATV owner’s manual for specific maintenance instructions. Always check the fuel lines, filter and gas tank for contaminants and clean as required at the same time to avoid further clogging.
The majority of carburetor problems are a result of blockage and worn out parts. Troubleshooting a clean ATV carburetor is also much easier than troubleshooting a dirty carb.
Typical tools required include a flat head screw-driver, compressed air, an 8mm wrench and carburetor cleaner. Note: Some gaskets and plastic components will swell if exposed to carb cleaner so remove these prior to use.
In order for the ATV to work like a clock, the rider needs to regularly carry out a complete maintenance of the equipment. And a key element of maintenance is ATV carburetor adjustment. Over time, the system starts to work incorrectly, which increases fuel consumption, worsens dynamics and other problems appear. So how do you adjust an ATV carburetor? nine0003
The operation and life of the engine directly depends on the quality of the fuel mixture. The carburetor is responsible for the preparation of the composition, but after prolonged use of the equipment, the settings “go astray”.
This results in:
Many riders who decide to buy an inexpensive ATV simply do not spare the technique and ignore this procedure.
But even if you plan to change your device in 1.5-2 years, adjustment is needed. The reason for this is increased fuel consumption. A quad with an untuned carburetor "eats" 30-40% more gasoline, and these are tangible costs.
So how do you adjust the carburetor on a Chinese ATV? For this you need:
However, it is important to remember that all adjustments are made only with a "clean" carburettor. This means that the rider needs to remove all the dirt from the node and flush the system to remove condensation and sediment from it.
Note: Just before adjusting, the engine must be warmed up to operating temperature.
To set the carburetor idle speed, the float chamber must first be cleared of fuel.
To do this, start the ATV, close the fuel cock and wait until the machine stalls (5-10 minutes). To speed up the process, you can take a little ride on the quadric. Of course, gasoline can be drained, but in any case you will have to warm up the device, so the first method of "removing" gasoline is more effective. nine0003
Then:
Focus on sound. The engine should run smoothly, without strain. Read the manual before adjusting the carburetor on a 125cc ATV to be sure. Remember that the location of the bolts is different in different devices, so read the documentation in advance. nine0003
To evaluate the quality of the fuel composition, make a test run. After that, unscrew the candle, and evaluate its condition. If it is:
And if the mixture is too lean, the whole candle will be white.
Also look out for these “symptoms”: damaged tip (electrode failure), oil deposits (damage to rings and caps), chips and inclusions (sign of motor failure).
To adjust the mixture you need to twist the needle cover and pull it out. To get the needle, pull out the cable. After that, move the ring in the required direction (lower - more air, but less fuel and vice versa). Then start the engine and make sure it doesn't stall. nine0003
The last step in adjusting the 125cc ATV carburetor is adjusting the petrol level. To do this, you need:
Note: Adjust as carefully as possible as system components are very fragile. Ideally, carburetor tuning should be done by a specialist.
06/16/2020 22168
It often seems like an insurmountable task for beginners to tune and adjust the carburetor of an ATV, but in fact, it is far from being the case. Using our instructions, you can easily set up a carburetor with your own hands. nine0003
Due to improper carburetor settings, problems such as: failures during acceleration, jerks while driving, uncertain start of the engine, poor acceleration dynamics, overheating, loss of power, increased fuel consumption, formation of deposits in the combustion chamber.
So what exactly are we going to tune?
Attention! The adjustment is carried out under the condition of a warm engine and a clean carburetor.
First, make sure there is no condensation in the carburetor. First, you need to drain the gasoline from the float chamber, for this you need to close the fuel cock and partially unscrew the screw No. 1, after the gasoline has drained from the float chamber, tighten the screw No. 1.
Let's look at photos of candles with various deposits and defects. nine0122
A 100% indicator of a correctly adjusted combustible mixture is carbon deposits on a candle.
Consider the location of the screws for adjusting the quality of the mixture and idle speed of carburetors of different models.
#1 Float chamber plug; No. 2 Mixture quality screw;
#3 Idle adjustment screw.
1 - quality adjustment screw at idle; 2 - fuel inlet fitting; 3 - fitting through which you can sleep fuel from the float chamber; 4 - screw-plug of the float chamber. nine0003
1 - ventilation tube; 2 - idle speed adjustment screw; 3 - screw for adjusting the composition of the air-fuel mixture.
ATV carburetor speed and mixture adjustment.
1. Start and warm up the engine until it reaches operating temperature.
2. Adjust the idle screw to set the idle speed to normal. Completely, until it stops, tighten the fuel mixture screw, the engine should stall. If this does not happen, check the tightness of the air supply system from the air filter.
nine0003
3. Loosen the fuel mixture screw 1 turn. (Turning the screw clockwise, we enrich the mixture, unscrewing it counterclockwise, we lean).
4. Start the engine and, by adjusting the idle screw, set the speed slightly higher than usual
5. Slowly unscrew the fuel mixture screw until the engine reaches maximum speed (we unscrew the screw no more than 2 turns, but depending range may fluctuate due to engine wear and other faults). nine0003
6. Re-adjust the idle screw to set the idle speed to normal.
7. Press the throttle trigger several times, check if the idle speed is stable.
Mixture quality adjustment with a needle.
Probably you have heard more than once about adjusting the quality of the mixture on the carburetor by manipulating the needle. I note that these are extreme measures, for the initial adjustment, use the mixture quality screw, and only if you do not get the desired result, unscrew the mount and remove the needle.
What does she represent? This is the main element that regulates the amount of gasoline supplied to the combustion chamber. Connected directly to the throttle handle through a cable. When you turn the knob, the needle rises higher, opening up a channel for fuel, thereby delivering more mixture, which increases power, which translates into speed. nine0003
You will see 5 grooves on the needle at the attachment point. Initially, the retaining ring fixes it in the central position, this is the best option. But sometimes it is not possible to achieve the required quality of the mixture. Then we will need the remaining grooves, 2 on top and 2 on the bottom, this suggests that we can adjust the dose gradually.
Lifting the retaining ring up and locking it in this position lowers the needle, which, in turn, blocks the channel more than usual. Gasoline enters less than air, and the mixture becomes leaner. Lowering the ring down, we raise the needle, and everything happens exactly the opposite.
