Fuel Injection - Dirt Rider Magazine

Face it, the carburetor-that great hole with its belly of gasoline and another bunch of smaller holes, a maze of passages, some brass pieces and maybe a few wires-is more dead than the two-stroke. Fuel injection is taking over. FI is here for two reasons: First and most importantly, the cost. The electronics that control the system have dropped in cost and size to where they are price competitive, often even less expensive compared to a carburetor. Second, the control that can be programmed into the FI systems can give all the advantages necessary for today's applications, everything from delivering flawless throttle control all the way to meeting ever-tightening emissions standards on non-competition bikes.You can hardly find a car or truck manufactured in the last 20 years that isn't fuel injected, so the writing has been on the wall a long time that the switchover was going to happen with motorcycles. It has been going on with the street side of motorcycles for at least the past 10 years. When spy shots from Japan first began showing FI motocross bikes, the rumor mill went into full effect, claiming fuel injection offered less power, no snap, poor throttle response, less rpm, stalling, clogged injectors and inexplicable electronic failures. Now that we've been riding more popular brands producing FI bikes for the last couple of years, those fears have largely diminished because the high performance is there. Sure, the first Cannondales and ATKs that boasted then-revolutionary FI systems had issues. But remember, that was a good decade ago. Shortly thereafter companies like Gas Gas and Sherco made the switch on some of their higher-end four-strokes. Next Montesa, which was actually an arm of Honda, made a bold step with the 2005 Cota 4rt in the trials world with a four-stroke battery-less FI system, which is now commonplace.

The Basics

Here is a layperson's explanation of the wonders of fuel injection. Basically there is a pump unit, usually housed in the gas tank, that pumps fuel to over 35 psi and then it goes straight to the injector nozzle. The nozzle is an electronically controlled valve, and it meters 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 that info and readings from other sensors (which vary from bike to bike) to measure readings like engine rpm, exact crank position, coolant temperature, air pressure, air temperature and oxygen content in the exhaust, the FI computer figures exactly for how long and when it should pulse and squirt fuel into the intake tract.And as complicated as that all seems electronically with all the variables, the actual working of the system is quite simple. FI performs the same functions a pilot, main, needle and nozzle were doing using their highly refined but very complicated system based on suction velocity. Now, we are doing it with ones and zeros pulsing electrons on a chip operating off a spreadsheet. The advantages are growing with every revision of software and hardware. The biggest advantage is consistency.

There are two types of FI systems on dirt bikes today, open- and closed-loop. What open loop means is the FI system does not make changes based on exhaust gas readings; it only factors in air pressure and temperature (and is what's found on most dirt bikes), so it is just a more accurate way of delivering fuel than a carb but limited on how much it can react based on constantly changing conditions. Closed loop means the system takes readings from an oxygen sensor and a mass airflow (MAF) or manifold absolute pressure (MAP) sensor, and corrects fuel mixture on the fly to make the air/fuel ratio exactly as prescribed. You can usually tell the difference visually by the presence of an oxygen sensor someplace in the exhaust system. The closed-loop system is especially convenient for vehicles that must pass strict emissions requirements while most race bikes only need to be open loop.


Tuning FI bikes is such a clean process, meaning no more gas on the hands while trying to figure how to get at jets and properly route all those vent hoses. Now, in most cases, with a simple plug-in tuner you can quickly and even drastically alter what you want and need your bike to do. There are two major changes you can usually make to most modern four-stroke ECUs: Fuel changes and ignition changes, since the ECU likely controls both. Some tuners let you adjust "transients" (to adjust for the rate of throttle position change, like the fuel pump squirt on a carb), and some even will do your jetting for you (optimization). Some allow you to change between multiple maps via a bike-mounted switch. Here are the basics of what some of the changes do:Ignition Timing: Typically this adjusts how responsive the bike is to the throttle and rpm. Advancing the ignition gives the feel of quicker or snappier pickup, and retarding it mellows the feel or slightly slows the pickup. If this is available, this is the easiest change for a rider to feel and the most dramatic in performance. Ignition timing changes are usually the first changes Dirt Rider will make to a bike, if it is available, when we are trying to change the feel of the power character of a bike.Fuel Tuning: This allows you to add or lessen fuel to the engine. Depending on the software, there are many ways of accomplishing it-in small throttle position or rpm segments or across the board. Assuming you're starting with a good baseline setting that is correct, going richer with the fuel you typically give the bike a feeling of more traction and a slightly slower pickup. It can also slow the speed at which the bike goes through the power. Leaning the fuel mixture typically makes the bike spin up easier and gives a sensation of a quicker-revving engine.Transients: This is the electronic "pumper" and can be used to give the bike more or less snap or make up for a slightly lean setting on a big handful of throttle. Generally, if you add more fuel with a transient setting, it will give the bike more hit. Less fuel is typically less hit or snap assuming it is correct where you started. Going too far in either direction has the opposite feeling completely, and FI systems can really compensate for improper tuning, meaning instead of the bike just stalling or bogging down, it will keep running, just poorly.Optimization: This is where an O2 sensor is hooked up to a data collection box, and it records the exhaust gases at different throttle positions and rpm. Then it shows what your "digital jetting" really is with an air/fuel ratio. You can adjust it manually or some systems will automatically make the correction on the fly when prompted. This is often a tool used when tuning on a dyno as well.


Here is a description of some of the more popular tuning tools and software Dirt Rider has had time to adequately test.

Honda $415.95/

The HRC Power Tuner tool is a good balance of complexity and usability allowing the user to "jet" the bike for just about any condition or tuning angle they might want. With full-range tuning of both ignition and fuel with stop limits put in place to make it difficult to blow up the bike, it is about as technical as most will ever need, having both spreadsheet and graphical three-dimensional representations of the changes you make. It requires the use of a PC laptop, a battery and the included wiring harness. The 2010 and newer bikes are much easier to access the plugs on. It is easy to make small changes quickly, but building complete maps takes some time and is best done before riding, so you can load them trackside in just minutes.Yamaha


Yamaha decided to make a palm-sized tuner, and the company has an easiest-to-use and very effective tool to adjust the bike as much as most riders need or normal modifications require. It is as plug-and-play as tuners come and requires only that you have good AA batteries. Maps can be changed in three rpm and throttle positions for both ignition and fuel. Although very basic, the changes are effective.Bazzaz

Z-Fi MX, $324.95;

Z-AFM, $299.00/

Bazzaz has entered into the dirt bike world after becoming well known in the street side of fuel tuning. Very similar to the Yosh system in concept, it piggybacks on the bike's stock wiring interrupting the standard signals and adding Bazzaz tuning. A preprogrammed fuel controller is the starting block with an altered fuel map (which will come preprogrammed for slip-on exhausts and will be offered in conjunction with FMF's full systems), and the system can grow to allow fuel optimization, allowing a proactive fuel map change if you want that level of performance. The target air/fuel map can be altered for throttle and rpm settings to get the feel a rider wants and will allow the best possible setting in conjunction with motor modifications or different track scenarios.Kawasaki


Kawasaki offers one of the most sophisticated systems available and it is a techie's dream tool. Not only will it allow changes to ignition and fuel maps in a pretty drastic range, it will also record data points 10 times a second while you're riding for more time than is practical, up to eight hours! Picking up readings on rpm, throttle position, gear selection, voltage, air and coolant temperature, you can basically see what you're doing around the track and see what throttle position and rpm might need changes, if the rider is able to place the data with the feeling they have. We had a number of riders who just couldn't put it together, usually because they swore they were wide open and the TPS showed more like 70 percent. All the values are shown in a graph form, and the time line can be adjusted to see very exacting detail.The fuel and ignition can be shown in a spreadsheet and in graphical form, both 2-D and 3-D, so you can visualize the changes. It is pretty easy to make complex changes at the track but requires a battery and the cable, a PC, as well as a data box that attaches behind the front number plate.


Power Surge 6X, $209.95/

The JDJetting tuner has six-way adjustments for both fuel delivery and mapping. Five settings adjust fuel flow rates, and the sixth setting adjusts mapping transition. The unit tunes in ranges similar to a carburetor, which helps riders that are new to EFI motorcycles. The Power Surge 6X tuner stays on the motorcycle, uses the bike's power supply and can be adjusted when the motor is idling. This allows for making fuel adjustments without tools at any time, just by stopping and pushing buttons. The adjustments help correct for fuel types, inaccurate sensors and incorrect factory mapping. JD says the factory mapping can only perform as well as the information that the sensors provide for temperature and air pressure, and the factory sensors have a hard time correcting for high humidity or drastic changes in fuel.Yoshimura

PIM-2, $339.95;

Data Box, $429.00/

Yosh's PIM-2 is a piggyback system that rides atop a stock FI system. The PIM will accept pre-made maps that alter only the fuel delivery of the stock system to be whatever (richer or leaner) is desired at any rpm or throttle position with the supplied software. It requires a computer and is very simple to change the fuel management or install the pre-made maps. Then there is the ability of the system, with a Data Box and an exhaust sensor, typically requiring a Yoshimura headpipe with the bung hole for the sensor, to record the exhaust gas air/fuel ratio and then display the correction factors it sees compared to the installed map. You choose a target air/fuel ratio through the entire map or at any specific zone. You can then decide to optimize the map to the new settings. You can alter and change the target air/fuel ratio and smooth the changes as well. Maps for the PIM-2 are available online.Dynojet

Power Commander V, $369.95;

AutoTune, $259.99;

LCD unit, $299.99/

The Power Commander V is a plug-in device that intercepts the signal to the injector and alters the fuel ratio through preprogrammed maps. A buildable system, it also has attachments for an optimizer, the AutoTune and components for other applications like a power shifter and instruments which show readings for rpm, air/fuel ratio, map, trim or throttle position. The software allows you to create customized maps, have the Power Commander optimize them for you and has the ability to change maps on the fly with the right upgrades. Dynojet has maps for its Power Commander available for download on its site.Dangers

Are there dangers in altering your FI settings and the standard maps in the ECU? Yes there are, but the changes are not out of line with being able to change the jetting in a carburetor and changing ignition timing like we've been doing since the days of points and condensers. As with anything, you can go too far and the results are the same, from poor running conditions to engine damage. Most tuners have built-in limits that make it very difficult to do anything catastrophic, and in reality the biggest challenge is making sure all the wires and connectors are secure and away from places where they can become pinched or burned. FI has a long track record of consistent, flawless performance on millions and millions of vehicles. It may be different for dirt bikes in the short term and present a new set of tuning and maintenance parameters with it, but fuel injection is pushing dirt bikes forward and it isn't looking back.