Imagine that you're riding out in the sand dunes of Utah. It’s 110 degrees you have little water left in your camelbak and you’re also having a food shortage. You just bought a 2014 fuel-injected Kawasaki KX450F, and you are on a 20 mile loop. Your bike stops running, and there’s no fuel combustion to give the motor power. One of the sensors of the fuel injection went out, and now the whole system has utterly failed. What is to be done? A computer is not within walking to distance to provide a system reboot. This is the constant fight with fuel injection. Carburetors and fuel injection (also known as EFI) consistently cause fights between motor heads.
Cars and Dirt Bikes both consist of the two common objects: an engine, and either a carburetor or a fuel injection. A common question that most may ask: “What is a carburetor?” A carburetor is a device in an internal combustion engine for mixing air with a fine spray of liquid fuel. “What is fuel injection?” Fuel injection is the direct introduction of fuel under pressure into the combustion units of an internal combustion engine. To an average human, this may seem like a useless topic, but to the gear heads, this is beautiful. The topic of carburetor versus fuel injection has been the highlight for years in the car industry. As it was meant to be, dirt bikes finally were able to see which system maximizes fuel combustion. The carburetor used in dirt bikes has more power, is less complex, and easier to maintain than a fuel injection is. Companies should continue making some bikes with carburetors and not completely switch to fuel injection.
Gear heads have been chomping at each other for years over the topic of, “Which combustion system is better for your bike?” Both of them have been competing in cars and bikes since the early 1900’s. Many questions always asked between fuel injection and carburetor was which produced more power, has much faster and better throttle response and which is the most cost effective. One reason why carburetors versus fuel injection has become a HUGE topic is due to fuel injection becoming a major part of the motocross industry. This is an important topic for those who are into racing motocross and even cars. It’s all about maximizing the performance of an engine, and for that the carburetor or fuel injection needs to be at their finest. This means either one needs to have the most power output, be the easiest to maintain, to be the one with the best fuel economy, etc. Fuel injection or carburetors should be able to come as the ideal package with all the above.
The world's first carburetor for the stationary engine was invented by the Hungarian engineers János Csonka and Donát Bánki in 1893 (Obuda University). The carburetor was most commonly used in dirt bikes up until fuel injection became popular in 2009. The goal of the carburetor is very simple: it needs to mix the correct amount of fuel and air for engine combustion. A carburetor consists of an open pipe through which the air passes into the inlet manifold of the engine. The pipe is in the form of a Venturi (a short piece of narrow tube between wider sections for measuring flow rate or exerting suction). It narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the Venturi is a butterfly valve called the throttle valve, this is a rotating disc that can be turned end-on to the airflow.
The throttle valve can be opened wide to allow complete flow, or it can be rotated so it almost completely blocks out the flow of air. This valve controls the flow of air through the carburetor throat and the quantity of fuel/air mixture the system will deliver. This will regulate the engine power and speed. Carburetors remain more basic compared to fuel injection. Not many technological advanced can be made to the carburetor, as the become more technologically advanced the combustion system would be more similar to the fuel injection.
Fuel injection was invented, or patented, as far back as 1896, but little work was done about the fuel injection systems until Robert Bosch developed working fuel injection systems to be used in diesel engines. By the 1920’s, it was widely used on diesels and during the 1930’s, German engineers developed fuel injection for gas engines used in fighter aircraft. This was a big step during these times, as fuel injection produced faster responsiveness than a carburetor, which was the difference between life or death during the World Wars. In the middle of war, being a fighter pilot the plane with the fastest system would always prevail. Originally carburetors were used in many fighter jets until fuel injection was introduced. This gave the Germans the upper hand due to them not suffering from “g” force that limited performance on carbureted engines (Second...Garage). When other countries realized that the Germans were technically “cheating” the system, they copied this idea and thus began the race of carburetor versus fuel injection.
Jimmy Lewis of Dirt Rider magazine talks about EFI in a much simpler scenario, saying, “Basically there is a pump unit, usually located in the gas tank, this pumps fuel to over 35 psi and then it goes straight to the injector nozzle. The nozzle is an electronically controlled valve, and it measures how much gas is released in a timed squirt. Fuel is pulsed into a throttle body where a butterfly valve is controlled by the throttle. The butterfly valve meters the amount of air that can pass through the throttle body. It has a position sensor to communicate information to the computer on the throttle opening.”
With certain information and readings from other sensors to measure readings like engine rpm, exact positioning of the crank, coolant temperature, air pressure, air temperature and oxygen content in the exhaust, the fuel injection computer figures exactly for how long and when it should pulse and squirt fuel into the intake tract (Lewis). As complicated as this all seems electronically, including all the variables and different parts, the actual working of the system is very simple.
Fuel injection performs the same functions as the pilot, main, needle and nozzle were doing except it uses its very own complicated system based on suction velocity. Now, professionals are doing these functions with zeros, which are pulsing electrons on a chip that operate off a spreadsheet (Lewis). The biggest advantage to using this spreadsheet is consistency, but the advantages are drastically growing with every reconstruction of software and hardware. Fuel injection also starts the combustion process much easier than a carburetor when in colder temperatures. In carbureted engines, the fuel/air mixture meets in the carburetor. The mixture then goes to each cylinder through the air intakes. In the fuel injected engine, the fuel and air do not mix until they reach the cylinder (Yoder). This makes a carburetor easier to start when the engine is overheating. A fuel-injected engine is easier to start in cold weather than a carbureted engine. The priming is more efficient and starting is more assured with less chance of an induction fire (Peterson’s...Inc.).
Carburetors are becoming less and less common in dirt bikes as the years progress. Mikuni and Keihin are two of the most common aftermarket carburetors used in dirt bike engines in the last 10 years. Mikuni’s new HSR48 (the letters stand for the model type and the 48 stand for the diameter of the carburetor measured in mm) was developed for large, highly tuned engines. It flows 26% more air than the HSR42 and 14% more than the HSR45. Highly developed engines with large valves and expert port modifications can gain peak power using the HSR48. Engines with stock ports do not benefit from the HSR48's greater flow (Mikuni). This means that for these aftermarket carbs to work at maximum efficiency, the ports need to be aftermarket and adjusted. This carburetor is used often by Team Honda and Team Yamaha.
The advanced technology found in Keihin CR Racing Carburetors has been proven in over twelve years of road racing with countless World Championship and National Championship Superbike victories. Following the superbike victories, Keihin has established a high reputation for its performance, reliability and quality. Having a tradition of advanced technology and performance, Keihin's latest carburetor design for racing is the FCR, which is designed for downdraft engine design use. The FCR features a flat slide throttle operating on roller bearings in a smoothbore Venturi (Keihin). This is the perfect racing carburetor for use on downdraft engines, as it is found in many popular sport bikes that are designed for serious competition. Keihin FCRs are the number one carburetor for use in many factory super bikes and endurance teams that use a, inline 4 cylinder engine. These carburetors are very popular among Team Suzuki and Team Kawasaki.
ACCEL DFI, Electromotive’s TEC System, FAST and MoTeC System are four of the most common aftermarket fuel injection systems on the market, as they are all reliable and extremely good. The ACCEL DFI system is the most popular and one of the most reliable aftermarket fuel injection systems available (Cars Direct). The Generation II version of the ACCEL system features idle air control, knock control, fueling control and acceleration management. It is available in different configurations, ranging from the basic system to the extensive system. For crate-engine combinations, (which is a replacement engine), the Generation II version also comes with a Plug-n-Play system. The Plug-n-Play system is a programmable electronic fuel injection. The settings can be directly changed by just plugging the system into the computer and programming to the specific need. It has the ability to operate 3 stages of nitrous oxide as well as calculate the amount of fuel enrichment for each of these stages. This is multi-tasking at its finest for a combustion machine.
Electromotive is second best to the ACCELL DFI. This fuel injection system is probably one of the most sophisticated systems that includes MAF-digital. The TEC system is expensive. It can set the buyer back at least $2,000 due to its patented fuel injection and direct ignition control, which are combined into one. This computer programmable control system features a window-based tuning system. Electromotive EFI system is available in TEC II and TEC III. The TEC III is an upgrade on the TEC II with the addition of a new processing platform. It has a patented digital Direct Ignition Control as well as anodized ECU that has waterproof OEM style connectors (Cars Direct).
FAST, which means Fuel, Air, Spark Technology is capable of converting your engine to an fuel injection system using a standalone system (it doesn’t require a operating system’s services to run on). Formerly called the Speed-Pro system, FAST was designed specifically for C-Com and PC Windows-based software. This makes for easy tune-ups and allows you to simultaneously look at timing curves, fuel maps, data logs and enrichment tables (Cars Direct). However, one of the best features of FAST is that you can tune the system via the Internet. All you need to do is plug in your computer or laptop to the ECU or a Electronic Control Unit, and provide the tuner with the IP address. It will then do the rest of the work by itself without needing somebody to give the computer direct instructions.
MoTec fuel injection system features a three dimensional fuel ignition control, and mapping. This feature enables the person using this to set the time for the spark, as well as drive the ignition modules at its maximum at all times. It has individual and injection cylinder fuel/ignition trims that can handle engines with eight cylinders. With its programmable flash memory chip, you can store programs without the need for a program chip or EPROM (Cars Direct). MoTec's mass air fuel injection system passes all emission testings, which means the EPA (Environmental Protection Agency) cannot interfere.
In 2014, Dirt Rider magazine did a combined test between carburetor and fuel injection. They tested the Jetting, Altitude Compensation, Complexity, Adjusting, Weight, Power and Feel in both carbureted and fuel injection combustion systems. With combined feel (how the bike feels when riding including power, smoothness, responsiveness) and power the carburetor pulled ahead of the fuel injection. The fuel injection contains more power ranging from 5,000 to 7,000 RPMs, but the carburetor has more power, anywhere from 7,500 to 10,000 RPMs (Dirt Rider). The carburetor also has more of an “organic feel” as opposed to the fuel injection. The throttle response is no doubt much faster all across the board when running a fuel injection system. The fuel injection has completely eliminated the horribly-awaited drag or bog that comes with the brass jets that are used in most carburetors.
Complexity and adjustments is another huge part of the struggle between the two. Fuel injection is very easy to adjust when it comes to having the computer next to you. Every adjustment is handled by the computer and the fuel maps can be reprogrammed by riders anytime the need arises— as long as you have the software. With a carburetor however, if you have the metric tools with you and something in the system seems to be failing, you can adjust the ports and float as simple as 1, 2, 3. The ports allow how much fuel is let into the carburetors reservoir, while the float is located in the reservoir and this is what sucks the fuel to start the combustion stage. Higher altitude is the best way to test which combustion system is easier to adjust.
Now with fuel injection, if the oxygen sensor, which is used to change how much fuel and air is being combined, there is no way to fix it without reprograming the system. The bike will run horribly with a worse throttle response than before. The bike may not be able to stay running since you cannot adjust the idle of the bike. With a carburetor you can adjust the idle and almost everything that comes with it. At a higher altitude, you want the best mixture of fuel and air, with tools you can adjust that. Now, fuel injection is not a horrible system, but when it comes to being able to work on your bike without the help of professionals, carburetor is the way to go.
Carburetor and fuel injection both contain many strengths and weaknesses. A carburetor produces more power at higher RPM’s. Fuel injection contains a much faster throttle response at all times. The carburetor also is easier to maintain with the use of tools, rather than the use of computer software. Fuel injection is less complex when comparing everything that goes into the making of the combustion system. The fuel injection system is an expensive system as well, as they can run from $1,000 to $2,000 based on brands and different hook ups.
Carburetors are not cheap systems either, the systems are still costly. A brand new carburetor for a 2010 YZ450R costs around $1,200. Both are expensive, but a carburetor can also be bought used but in mint condition. Cost and maintenance on carburetors are just part of how they dominate fuel injection. Adjustments on a carburetor are much easier as said before. With the use of tools you can adjust how the bike runs at a higher altitude. If a bike was normally ran in Hotchkiss, Colorado (around 5,300 feet) then ran at a high altitude such as Taylor Reservoir (10,000 feet) located just north of Gunnison, Colorado the jets could be adjusted or known as “re-jetting”. Adjusting the jetting changes how much fuel is being sprayed through the jets, which will change how the bike will run at different elevation. If you have fuel injection, however, the oxygen sensors will detect the different levels of oxygen and adjust how much fuel is being sprayed through the nozzle.
Both of these systems are complex, but they also both provide exactly what they were designed for — fuel combustion to give a motor power. Both systems have positives and negatives, but overall the carburetor pulls ahead of fuel injection. It produces more power at higher RPM’s, it is much easier to maintain and is way less complex than the “godly” fuel injection. When it comes to saving your money where it counts, longevity of the combustion system and more raw power, the carburetor by far is the best bang for your buck.
”Black & White: Is Fuel Injection a Blessing or a Curse?." Motocross
Action Magazine. Hi-Torque. Web. 27 Feb 2014.
"Cars Direct." 4 Top Aftermarket Fuel Injection Systems: Ratings and
Reviews. 27 Jan 2013. Web. 16 Mar 2014. <http://
Dumitrache, Alina. "Auto Evolution." Motorcycle Dilemma: Carbureted Vs.
Fuel Injected. 20 Aug 2010. Web. 7 Mar 2014. <http://
Lewis, Jimmy. "Dirt Rider." Fuel Injection. 03 Feb 2011. Web. 7 Mar 2014.
"Mikuni American Cooperation." Carburetors. 24 Mar 2002. Web. 24
Mar 2014. <http://www.mikuni.com/fs-carburetor.html>.
"Obuda University." Donat Banki. Web. 4 Apr 2014. <http://www.uni-obuda.hu/e
"Peterson's Performance Plus, Inc." A Fuel Injected Engine is Hard to Start. Web. 4 Apr
"Second Chance Garage." A Short History of Fuel Injection. Web. 4 Apr 2014.
"Sudco Keihin Carburetors." Flatslide CR Downdraft/Sidedraft Carbs. 24
Sep 2013. Web. 24 Mar 2014. <http://www.sudco.com/
Tracy, David. "Jalopnik." How a Carburetor Works. 13 May 2013. Web. 7
Mar 2014. <http://jalopnik.com/how-a-carburetorworks-4963948>.
Yoder, Myron. "Sweet Aviation." Engines: Carbureted vs Fuel Injected. Web. 4 Apr 2014.