Motocross EFI Tuning Essentials - Dr. Dirt

Fuel injection (FI) has become the preferred way to deliver fuel on four-stroke motocross and off-road motorcycles. It provides better throttle response, aids starting, allows the engine to run smoother and operate better when temperatures and altitude change, and even improves gas mileage. Despite the downsides of added weight and cost, the basic operation and ease of tuning are a major advantage over a carburetor.

A fuel-injection system works by pumping fuel to an injector that sprays it into a throttle body. The ECM (Electronic Control Module) sends a signal to deliver a precise amount of fuel after receiving information from sensors. The sensors monitor a number of things, including crank position, throttle position, engine temperature, air temperature, and barometric pressure.

FI systems are tuned by either accessing preprogrammed air/fuel/ignition maps in the bike’s ECM or creating and loading custom maps to the ECM from an external device. By altering the air/fuel mixture and ignition timing—across the entire rpm range—the bike’s power characteristics can be optimized for track conditions or rider preference.

Fuel mixtures can be altered to deliver more fuel (rich) or less fuel (lean) to the same volume of air. Bikes often come from the factory with slightly rich fuel mixtures to increase reliability (they run cooler when tuned slightly rich). Power can be increased by leaning the mixture to an air/fuel ratio somewhere around 12.5–13.0 to 1. The reverse is true when a bike is tuned overly lean from the factory to pass strict emission tests. The fuel mixture can be then richened to regain lost power, but that often renders the emissions-restricted bike a closed-course-only vehicle. In other cases, fuel is often added (richening the air/fuel mixture) at the bottom of the rpm range to prevent stalling and smooth out the power delivery in those lower rpm.

Ignition timing can be set to ignite the spark plug before (advance) or after (retard) the manufacturer’s specified piston position. We usually advance the timing to produce more power. Advancing the timing is often used when there is a lot of traction available. However, when the timing is advanced too far it can cause the engine to run rough and knock. Most tuning systems set fail-safe parameters so engine damage will not occur. Retarding the timing is often employed to soften the power delivery and is used in hardpacked and slippery conditions. It can be a big help to novice riders when a smooth power delivery is preferred or when converting a motocross bike for off-road use. Retarding the timing also makes the bike quieter. Many of today’s tuning systems allow timing to be varied over the rpm range. For example, it is possible to tune for smooth power off idle, a moderately powered midrange, and a high-powered top end.

Suzuki RM-Zs contain three maps inside their ECM. Every new RM-Z is supplied with two different-colored couplers that enable you to change the fuel map. The couplers simply plug into the stock wire harness behind the left-side shroud on 2014 models. Snapping in the white coupler leans the stock fuel mixture 3 percent throughout the entire rpm range. Snapping in the gray coupler richens the stock mixture 3 percent. Suzuki couplers do not modify the ignition curve from stock. In most cases we have found our best results using the lean coupler on both 250s and 450s. The exception to this has been in very cold conditions. RM-Zs can also be further modified with Yoshimura’s MX Tuner. The device plugs into the stock wiring harness and allows both fuel and ignition timing changes. A 12-volt battery is required to power the unit.

Kawasaki KX-Fs are also supplied with two different-colored couplers to change fuel-injection settings that are preset in the ECM. On 2014 KX-Fs the couplers are located on the right side of the frame behind the head tube. The white coupler provides more aggressive power for soft, loamy track conditions by advancing the timing and leaning the fuel mixture. The black coupler provides smoother power for hardpack conditions by retarding the timing and richening the fuel mixture. Our test riders preferred the stock or black coupler on the KX450F and the stock or aggressive white coupler on the KX250F.

Kawasaki sells a Fuel Injection Calibration Kit (part No. 99999-0394, retail $679.95) to fit 2014 KX-Fs that includes seven preprogrammed maps and also enable the user to make their own custom map. The kit has a logging function that gives data acquisition for throttle position, engine rpm, gear selection, engine temperatures, and more. The program has built-in parameter limits to prevent engine damage so timing cannot be advanced more than 4 degrees and fuel mixture cannot be leaned more than 10 percent from stock. A PC computer and 12-volt battery are needed to run the kit. The ECU controller can be mounted directly to the bike for quicker mapping changes. Kawasaki makes kits to fit fuel-injected KX-Fs from previous years.

Like Suzuki and Kawasaki, KTM SX-Fs also contain three preset maps in their ECM. The KTM Power Parts Motor Control Selector (part No. 76511010000, retail $66.59) plugs into the wire harness from the ECM and allows you to change between one of the three maps by turning a dial. By setting the unit to 1, an easy power map is activated, 2 activates an aggressive map, and the stock map is 0. KTM also offers a Handlebar Map Selection Switch (part No. 77239974000, retail $145) that allows you to change the map on the fly. The handlebar switch only allows changes between the stock map and one other map. You simply select the second map of your choice on the Motor Selector. The handlebar switch will activate either the stock and easy map or the stock and aggressive map. These parts also fit on KTM two-strokes and function the same. On the 250 SX-F and 350 SX-F the stock and aggressive settings were preferred. On the 450 SX-F the stock map was preferred.

Also available from KTM is a Fuel Injection User Setting Tool (part No. 69029096140, retail $499.99) to enable the user to make custom maps. It is virtually identical to Kawasaki’s since it is also produced by Keihin, the maker of the throttle body and fuel pump. It requires a PC computer and a 12-volt battery source.

The Yamaha GYTR Power Tuner (part No. 33D-H59C0-V1-00, retail $279.95) is a handheld unit that allows the user to create custom maps without a PC or 12-volt battery source. Instead, it is powered by two AA batteries. The GYTR tuner is far and away the easiest and most practical unit for creating custom maps. It plugs into the wire harness behind the left-side shroud. By using nine adjustment points to change both fuel mixture and ignition timing, fuel mixtures can be varied up to 14 percent rich or lean, and ignition timing can be advanced up to 4 degrees and retarded up to 9 degrees. The memory can store nine maps at a time and it can read your current map if you forget what you programmed. There is a monitor setting that allows the user to see engine run time, engine temperature, and also run a self-diagnosis. The same tuner will work on 2010–’14 YZ450Fs, 2014 YZ250Fs, and 2013–2014 WR450Fs.

Recommended maps for each model can be found at yamahamotorsports.com. We had our best results using the “smooth delivery, longer power feeling” setting on the YZ450F.

Honda sells a PGM-FI Setting Tool to tune the EFI on CRF250R (part No. 38880-N1C-770, retail $459.95) and 450R (part No. 38772-NX7-010, retail $415.95) models. The kit includes a wiring harness interface and CD that varies between models and years. Changes can be made to both fuel and ignition mapping with custom maps (the systems have no pre-built maps included). It requires a 12-volt battery source and can be operated by a PC or Mac computer.

Getting into your bike’s electronics can seem intimidating, but once you test a few settings you’ll soon be swapping new maps way faster (and cheaper) than bolting on a new exhaust. Don’t forget, you were probably afraid to “mess with” your carbureted bike’s jetting at one point in time!