Motorcycling - Knowledge

Learn How to Tune Bike Carburetor for Mileage

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Do you have to increase the throttle each time so as to get your engine started? Does the engine tend to overheat even when you haven’t raced it that much? Or, has your bike lost that smooth acceleration that it had earlier? All such situations might be possible and they aren’t the favorable ones. Nobody wants their bike to perform poorly. So, what can you do in such situations? Well, tuning your bike might be the best possible option so as to improve the efficiency and performance. Setting and tuning to push the correct mixture of fuel and air would help in extending your bike's engine life. This tuning is done with the carburetor and most people often wonder as to how to tune it?

Well, the great thing is adjusting this carburetor is quite easy and doesn’t require any special tools. This guide aims at helping you to tune your bike so that it can deliver its best. 

Table of Content

  • Carburetors: How they Work and Basic components of a Carburetor
  • Anatomy of a Float Chamber
  • Understanding the Basics of Tuning Your Bike Carburetor
  • How to Tune Bike Carburetor for Mileage
  • How to Increase Bike Mileage
  • Summing Up

Carburetor: How it Works 

To answer the question as to how to tune bike carburetor for mileage, you first need to understand everything about the carburetor. The carburetors supply fuel to the engine with the help of a phenomenon which is referred to as Vacuum Venturi Effect. Air makes its way into the carburetor through the air intake and then speeds up drastically because of the narrow interior walls of the carburetor.

The air blows perpendicular into the throttle slide which is basically a valve that is controlled by the throttle cable. As soon as the throttle is opened, the throttle slide is raised with the help of the cable. 

As this slide begins to rise, the air pulls the fuel up the main jet through the float chamber. The fuel then gets mixed with the air and makes its way to the engine. The amount of fuel that flows in is completely dependent on the size and position of the needle, fuel level’s height and the size of the main jet. 

More air is forced through the venturi tube in the carburetor when more throttle is applied to the vehicle. This helps in drawing more fuel into the engine. 

As the vehicle ages over the years, it may develop vacuum air leaks from the various vacuum lines that are present in the engine compartment. These leaks present in the tube can lead to additional air being drawn into the intake manifold. This changes the volume of air or fuel mixture from the perfect blend to a more lean mixture. This, however, is a very common issue and can be resolved quite easily with carburetor tuning. 

carburetor working
How a Carburetor Works

Anatomy of Float Chamber

Now that you know how a carburetor works and its basic components, it’s time to know about float chamber and its parts. 

The float chamber is basically a reservoir for the fuel and generally, contains all of the working components of the float. You would notice that in most modern bikes, the float chambers are attached to the carburetor base. Also, a drain would also be fitted to measure the length of the fuel or in general for maintenance purposes. 

If you look really carefully into the float chamber, you would be able to find the float. This is the device that is responsible for controlling the amount of fuel that would enter the float chamber. 

Components of Float Chamber

  • Floats 
  • Needle valve assembly
  • Float pivot Rod 
  • Drain Plug 
  • Chamber and Gasket 

The Float and Needle

As discussed above, the bike carburetor has floats. Now, these are made up of either plastic or brass. The float chamber works like a toilet tank and the floats basically float in the fuel. When the fuel is drawn up to the jet, the level of fuel present in the chamber basically drops. Henceforth, the float drops too. 

When this happens, the needle valve would open up and this would give way to more fuel. Now, when the float rises with the fuel level, the needle valve would close the supply of the fuel. 

how to tune bike carburetor for mileage
Inside Float Chamber (source)

Symptoms of Incorrect Float Heights

There might be cases wherein if the floats are set too high. If this happens the fuel would overflow via the drillings present inside the body of the carb. The fuel might even flow into the engine. In case the engine is in a stationary mode, it can lead to hydraulic lock. 

However, fuel leaking from the carb isn’t a good sign and can lead to a serious issue like fire if left unresolved. If the bike is running and the height of the fuel level is way too high, the engine would display a rich running condition.

This, in turn, would make the response of the throttle rather slow and the engine note muffled. If this ever happens, you would notice a very strong and unburnt smell of the fuel coming from the muffler. 

However, if the fuel is way too low, the engine would start showing a lean running condition wherein the engine typically would hesitate before starting. 

Understanding the Basics of Tuning Your Bike Carburetor 

If you find that your engine is running too rough, it might be time to look into the matter and take corrective measures. Before we begin, it is essential that you know the fundamentals. 

As its quite obvious, each bike has an engine and a carburetor. This carburetor is basically the heart of your bike. In this guide, we are going to assume that your engine isn’t damaged and isn’t dead. 

Now, you must definitely be aware as to where your bike carburetor is. To get started, what you need is a basic screwdriver in hand. Also, before you do this, your bike must have finished a minimum of one service –500 kilometers or more on the odometer.

To correctly notice the improvements after tuning remember to not change the fuel type that is Speed, Power, Normal Unleaded, Extra Premium etc. Run the bike on the same fuel type so you can assess the improvements made by tuning correctly. Now let's get going to how to actually do the tuning.

How to Tune Bike Carburetor for Mileage

Now that you are enlightened with bike basics, let’s learn more on how to tune bike carburetor for mileage:

Warm up the Engine

First, you would be required to warm up the engine nicely. Simply, ride your bike for approximately 5 minutes. Once, that is done, you are ready to begin the process.

Livingit Tip-
If your engine doesn’t warm up properly, you would get a bad tuning.

Locate the Air or Fuel Screw

The fuel and the air screws are the ones that assist in adjusting the air-fuel ratio. There is also another screw that sets the engine's idle speed. The idle screw is in no way going to help with the mileage or the pickup of the machine but does help in setting the rpm of the engine at an idle run.

But, how to know which machine has fuel screws or air screws?

Well, remember one thing - the two-stroke bikes have an air screw while when working with 4 stroke bike carburetor tuning, you would notice that it has fuel screws. 

The fuel screw is located on the carburetor and is very near to the engine. When you turn the fuel screw clockwise, it would give you a lean mixture and when it is turned anti-clockwise, it would produce a rich mixture. 

bike carbureto
Fuel Screw of Bike Carburetor (source)

The air screw, on the other hand, is also located on the carburetor but is away from the engine. The air screw when turned clockwise gives a rich mixture and when is turned anti-clockwise, would produce a lean mixture. A rich mixture means more of the fuel and less of the air. A lean mixture means more of the air and less of the fuel. 

If your bike carburetor is Mikuni made, the air or the fuel screw would be made up of brass and would be of a golden color. The idle screw is very closely connected to the with the throttle cable. For this, depending on the bike, you wouldn’t require a screwdriver. It can simply be turned with your hands. Keep the bike running when changing the idle screw setting.

Tune the Engine for Improved Efficiency 

Now, turn the idle screw in such a way that your engine it reaches approximately 3000 rpm. Once you have done that, slowly tune the fuel or air screw (whichever one your bike has) so as to make the mixture as lean as possible. As the mixture becomes more and more lean, the RPM of the engine would simultaneously begin to decrease. 

  • You must tune the screw until the air or the fuel screw has reached its maximum leanest point. The idle-screw would also need to be turned a bit so as to make sure that the engine doesn’t stall. When you are doing all of this, you would notice that the RPM of the engine isn’t stable at this point. This would be quite evident from the tachometer or the engine sound. 
  • Now, the next step would be to turn the fuel screw in an anti-clock direction which would be quarter to 1/8th turn at each time. As you keep on doing so, you would notice the RPM rising gradually. Remember to keep a steady hand and do things really slowly. When you are turning the screws, keep a count. The RPM would become constant once the screw has been turned for about 3 to 4 times. Stop turning the screw further as this is perhaps the ideal setting for your engine. 
  • Once you notice that the engine is running smoothly, decrease the idle setting screw in order to get the engine running at about 1000 RPM. You would need to twist the throttle if the engine slows down. The response should be quick and crisp.
  • Shut the engine off and restart. This time your engine would start in a single kick. If it does, your setting is fine. Take your bike for a ride and you would be able to notice the difference in the throttle response and engine sound. 

How to Increase Bike Mileage

The above steps would work just fine for how to tune bike carburetor for mileage, but if you are still wondering as to how to increase bike mileage, there are a few other things too that you can follow.

Listed below are a few of them:

Increase the Intake of Air 

This is perhaps the easiest method to enhance the performance of the bike. You could even use a mushroom head which would aid in increasing the air intake by about 50 percent. Remember to use an aftermarket mushroom head as that would offer an optimal balance of increased airflow and air filtration for better performance. 

However, this also means that more fuel would be consumed because of the thin air mixture. You can of course adjust the carburetor of your bike by making a slight adjustment to the air mixture screw, high and low speed air mixture ratio adjustment and by normalizing the air mixture ratio. 

Ignition Modification

Are you aware of what an ignition modification does? Well, it aids in generating the spark energy that is required to ignite the fuel or air mixture in the engine’s cylinder.

The main components of the system are: distributor, ignition coil, spark plug wires, coil driver and spark plugs. 

In case the ignition control angle is rather small in your bike, you should consider changing it. In such situation, you can either opt for an igniter that has a bigger control angle or just make use of a better spark plug. 

carburetor tuning for fuel economy
Ignition Wiring (source)

Switching Your Exhaust

When you choose to modify your exhaust system, you would be able to enhance your bike’s appearance, performance and sound. There would also be a reduction in the weight off your bike which means you might be able to gain a few horsepower depending on the exhaust. The aftermarkets exhausts available are made up of various materials like carbon-fibre, titanium as well as other lightweight materials. Therefore, it is essential to ensure that it fits and works properly on your bike. 

Now there are two options that you can choose from. You could either change the entire exhaust system or simply get rid of the muffler and add a slip on. If you choose to change the entire system, you would be able to get a much higher end power. However, with just a slip-on exhaust, it would give you an increase in the lower end power. While you are working on your exhaust system you might want to learn about using an exhaust wrap.

The next time when you are on your beast and if it doesn't give you the adrenaline rush, then you better start tuning the bike. The performance of your bike is definitely something that you should be concerned about. However, if it isn’t performing as well as you expected to be, you can try out a few modifications yourself. This would surely give you the desired results. We hope you have learnt how to tune bike carburetor for mileage. 

Share your tips and ideas on how to tune bike carburetor for mileage in your comments below. 

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