1995 Suzuki Savage LS650 Carburetor

The 1995 Suzuki Savage LS650 is a cruiser-style motorcycle built with a single-cylinder engine. Due to when it was made; the Suzuki Savage was made with a carburetor to control the air to fuel ratio rather than having a fuel injected system. Carburetors are becoming less and less common due to the fact they are less efficient, not as environmentally friendly, and overall, more tedious to work with compared to a fuel-injected system (RevZilla, 2022). While fuel-injected systems are better, the carburetor is still an incredible piece of machinery that has genius engineering in its making. Despite it’s relatively simple mechanical build, it performs a complex task consistently well (RevZilla, 2022).

Figure 1. 1995 Suzuki Savage LS650 Carburetor.

The Float Chamber

 The float chamber includes the carburetor bowl, the float, the float pin and valve, the main jet, and the pilot jet. The purpose of this section of the carburetor is to take in fuel and control the fuel amount entering the venturi air inlet.

Carburetor Bowl

 The carburetor bowl’s exterior is the outside of the float chamber shown in Figure 2. On the inside is where fuel enters the carburetor and where a small amount is stored as shown in Figure 4. The carburetor bowl, shown in Figure 5, is attached to the carburetor by four screws, and in between this connection there is a thin gasket that prevents leaks visible in Figure 5.

Float

 Inside the carburetor bowl is the float which is a hollow piece of brass that contains air shown in Figure 3. When fuel enters the carburetor bowl, the float floats on top of the fuel, hence the creative name of the part. The float is connected by a small metal pin shaped like a nail that holds the float in place but allows it to go up and down with the fuel level moving like a door hinge shown in Figure 4.

Fuel Inlet Needle and Valve

In the center of the float there is the fuel inlet valve where fuel enters the carburetor. Hanging from the float, resting inside the valve, is a very small cylindrical piece of metal with a cone shaped piece of rubber that is attached to the tip of it. This is the fuel inlet needle. Once the float raises to a set level, the float pin is pushed into the valve plugging it like a cork which prevents more fuel from entering. When there is very little fuel in the carburetor bowl, the float touches the bottom of the carburetor which in turn pulls the fuel inlet needle out of the fuel inlet valve, allowing more fuel to enter the carburetor bowl. This movement is what controls the amount of fuel entering the carburetor. This mechanism constantly adjusts with the fuel level the entire time the engine is running. These components are removed from the carburetor in Figure 4.

Main Jet

The main jet is located at the top of the float chamber and connects the region between the float chamber and the venturi air inlet shown in Figure 6. This is where most of the fuel moves from the float chamber to the rest of the carburetor. The main jet is a brass tube that allows for the needle of the vacuum piston to enter which is how the float chamber and vacuum chamber work with each other to control the air and fuel mixture ratio which you can see removed from the carburetor in Figure 11. It is held in the carburetor by the main jet screw and has a washer shown in Figure 7.

Pilot/Low-Speed Idle Jet

            The low-speed idle jet, shown in Figure 10, is a small brass screw with a hole in the center that allows for fuel to enter the Venturi air inlet even when the throttle is either not engaged or very slightly engaged. The throttle is the mechanism located on the right handlebar on a motorcycle that is used by the rider to make the motorcycle drive faster. It is the same concept as the gas pedal in a car.

Figure 6. Close up of interior of float chamber. Figure 7. Carburetor with piolet/ low-speed idle jet in front. Figure 8. Carburetor with main jet screw in front. Figure 9. Main jet screw. Figure 10. pilot/ low-speed idle jet. Figure 11. Main jet.

Idle Mixture Screw

The idle mixture screw is another brass screw, but this one can be adjusted on the exterior of the carburetor shown in Figure 12. It has its own small spring and rubber washer in place to make sure the screw does not move when it’s looser, so it doesn’t leak fuel. It works very similarly to the low-speed idle jet since it also allows fuel to enter the venturi air inlet however this is for when the engine is idling. When the screw is loosened more fuel is allowed through and the engine idles at a higher RPM (repetition per minute); when it is tightened, the engine idles at a lower RPM. This allows for the carburetor fuel to air ratio to be altered without having to take apart the whole carburetor to change it. Carburetors are temperamental when it comes to this fuel and air ratio problem because it must be set manually. The engine running rich means the ratio has too much fuel. The engine running lean means that the ratio is too low on fuel. Without a proper fuel ratio to the engine, the engine will not run properly. Typically, the rich and lean issue is not that significant because the ratio is usually very close to ideal and won’t prevent the engine from starting up, but it will cause minor issues. A minor issue with a rich engine is not all the fuel will get used up so when the waste gas from the engine moves to the exhaust to, it will also contain unused fuel which explodes in the exhaust pipe and makes a loud popping sound. This sounds much worse than it is, and it typically is just noise and doesn’t cause any significant issues as long as the excess fuel is in small quantities. When the engine is running to lean the most common issue is that the motorcycle will not go fast enough. For example, you wouldn’t be able to drive faster than 30 MPH (miles per hour) if the engine was running that short on fuel.
The idle mixture screw can be seen removed from the carburetor in Figure 13.

Figure 12. Close up of Idle Mixture Screw. Figure 13. Idle Mixture Screw.

Vacuum Chamber

Vacuum Chamber Cover

At the top of the carburetor there is a metal cap that is held onto the rest of the carburetor by four screws as seen in Figure 14. This cover accompanied by the body of the carburetor provides an air chamber for the other components. This is shown after it is removed revealing the interior of the vacuum chamber in Figure 15.

Vacuum Piston

The vacuum piston, shown in Figure 17, is a hard plastic hollow cylinder that holds the needle that goes into the main jet and the diaphragm that creates the vacuum. This piston is another dynamic part of the carburetor that moves constantly while the engine is running. The body of the carburetor has an open cylindrical port called the slide vacuum port that connects the vacuum chamber to the venturi air inlet. This is where the vacuum piston rests and at the bottom of the slide vacuum port is the entrance to the main jet where the needle on the vacuum piston enters.

Diaphragm

The diaphragm is a thin rubber bowl that is attached to the top of the vacuum piston shown in Figure 17. The diaphragm is what helps create the vacuum effect to the top of the chamber that the carburetor needs for the vacuum piston to move. Due to its flexibility, it can be suctioned to the top of the vacuum chamber as well as released of that vacuum seal in order for the vacuum piston to remain moving and adjusting the air portion of the air to fuel ratio.

Slide Spring

The slide spring is a large spring, shown in Figure 16, that goes through the vacuum piston to the vacuum chamber cover and keeps the vacuum chamber unit in place. It also provides a kickback system that allows for the vacuum piston to move back to its resting position and continue moving back and forth to maintain the proper air ratio.

Jet Needle

The jet needle is a needle that is connected to the bottom of the vacuum piston that goes through the main jet of the carburetor. This is shown in Figure 17 at the bottom of the vacuum piston unit. This is the same needle that goes through the main jet.

Figure 14. Top of Vaccuum Chamber. Figure 15. Vacuum chamber cover removed exposing vacuum piston, diaphragm, needle, and slide spring. Figure 16. Slide spring removed. Figure 17. Vaccuum piston diaphragm, and needle unit removed.

Air Jets

Located in the vacuum chamber there are two jets that control the portion of air in the fuel to air ratio. The main air jet is larger than the pilot air jet, but both serve the exact same purpose as the main fuel jet and the pilot fuel jet but instead of fuel, it is used to control air (suzukisavage, 2004).

Figure 18. View of inside the vacuum chamber. Figure 19. Main air jet. Figure 20. Pilot air jet.

Venturi Air Inlet

 The air inlet in the center of the carburetor is dependent on CC (cubic centimeters) capacity (the volume capacity of engine), type of engine, and engine speed (RevZilla, 2022). The whole carburetor process functions by the creation of a vacuum; in the engine of the motorcycle, a low-pressure vacuum is created by the piston inside the cylinder (madeinitalycustoms, 2016). Which is what pulls fuel and air out of the carburetor powers the entire function of the carburetor. The venturi air inlet is where the air and the fuel mix together and are sent to the engine and is shown in Figure 21.

Choke

The choke is a metal pin with a plastic disk at the end that protrudes outside of the carburetor shown in Figure 25. The choke has a very similar functionality to the idle mixture screw where regardless of whether or not the throttle is engaged, it allows fuel to go through the carburetor into the engine. When the rider pulls the choke out, it gives more fuel to the engine. The choke is only engaged when the engine is starting up and only when it is necessary. It is typically necessary when it is cold outside because it’s harder for the engine to heat up. To make it easier for the engine to start up in these conditions, the choke is pulled out giving a higher fuel level as compared to the air level to the engine making the engine burn hotter and in turn making it easier to start. Once the engine is up and running the choke is disengaged by being pushed back in and the carburetor fuel to air ratio functions like normal again.

Butterfly Valve

The butterfly valve is a brass disk located inside the venturi air inlet. It is set at a tilted angle and rests at a close. The Throttle cable is connected to this butterfly valve and has a spring that allows for the butterfly valve to stay in place in rest shown in Figure 23. When the throttle on the motorcycle is activated, it pulls that cable and opens the butterfly valve shown in Figure 24. The throttle mechanism is shown in Figure 25.

Figure 21. Venturi air inlet. Figure 22. Close up of venturi air inlet showing where the main jet connects to it. Figure 23. Other side of venturi air inlet showing butterfly valve resting. Figure 24. Butterfly valve engaged. Figure 25. Location of the choke and where throttle cable connects to control butterfly valve.

How All the Components Work Together

           When the butterfly valve is closed, it closes before the slide vacuum port, so no low pressure is applied to the vacuum chamber until the butterfly valve is opened when the throttle is activated (madeinitalycustoms, 2016). When the butterfly valve is open, the air is suctioned out of the vacuum chamber and pulled into the engine through the slide vacuum port. It sucks in air from the vacuum chamber causing the diaphragm to be pulled upwards and since it’s made of rubber it can suction to the top of the carburetor pulling the whole vacuum piston upwards. As the jet needle is raised, the Venturi air inlets Venturi shape (an hourglass-like shape) allows air and fuel to be suctioned up more efficiently from the air and fuel components. This allows the fuel and air mixture to be suctioned into the motorcycle engine (madeinitalycustoms, 2016). This is the main circuit of the carburetor which means that this is mainly how the fuel and air mixture is received by the engine because this circuit is performed when the throttle is engaged.

           In the carburetor there is another circuit that allows fuel to get to the engine without the throttle being engaged. This is needed when the motorcycle is not moving, which is called idling. The carburetor bowl, as discussed earlier, has a pilot/ low-speed idle jet that allows for fuel to enter the engine without the butterfly valve opening. This is also powered by the low-pressure created by pistons in the engine as mentioned before (although this time it is constant) (madeinitalycustoms, 2016). When the throttle is not engaged there is still a low-pressure vacuum being created through the piston valve and is shut off to the other parts of the carburetor via the butterfly valve. When the engine is in this position it only receives fuel through the pilot/low-speed idle jet. This passageway that the fuel goes through is interrupted by the idle mixture screw and is closed when the screw is tightened and opened more when the screw is loosened. This is how the engine can still run when the throttle is not engaged (madeinitalycustoms, 2016). Figure 26 shows how the carburetor components all work together to paint a better picture of how the fuel and air is mixed and sent off to the engine for use. Figure 27 is an overview of the carburetor construction and shows what it looks like with all the components removed at once.

Figure 26. Showing the dynamic function of the carburetor. From “Carburetor diagram”, by ThumperTalk, 2012 (https://www.thumpertalk.com/forums/topic/984396-carburetor-diagram)

Figure 27. Showing the expanded view of the carburetor. From “Carburetor Specifications” by SuzukiSavage.com, 2004 (http://suzukisavage.com/cgi-bin/YaBB.pl?num=1098869040)

References

Amazon.com: 1pz HX3-C01 carburetor carb replacement for … Amazon. (n.d.). Retrieved March 28, 2022, from https://www.amazon.com/1PZ-HX3-C01-Carburetor-Replacement-Fourtrax/dp/B07B7JHKMF

Carburetor diagram. ThumperTalk. (2012, September 29). Retrieved March 28, 2022, from https://www.thumpertalk.com/forums/topic/984396-carburetor-diagram/

Carburetor Specifications. Suzukisavage.com – Carburetor specifications. (2004). Retrieved March 29, 2022, from http://suzukisavage.com/cgi-bin/YaBB.pl?num=1098869040

madeinitalycustoms. (2016, February 23). How does a CV carburetor works – quick and simple explanation. YouTube. Retrieved March 28, 2022, from https://www.youtube.com/watch?v=IBFq9nHVmks&t=51s

RevZilla. (2022, March 28). How does a carburetor work? RevZilla. Retrieved March 28, 2022, from https://www.revzilla.com/common-tread/how-does-a-carburetor-work