KLR650 fuel injection? Used to be a novel concept but now its done and done properly.


In a quest for efficiency and better performance we decided to tackle the KLR650 fuel injection project head on. Based on calculations a fuel injected KLR650 can produce about 85 hp to the crank and compete with some of the more exotic bikes out there. We are not talking suspension here, only performance.

We want to put together a kit that will allow full control of all engine function. It must be reliable and increase engine performance without sacrificing ride ability . Because of tune-ability a  higher compression ratios can be used to run lower octane fuels. The kit will therefore include an engine setup with a 10.5:1 compression ratio.

Basic components required for the KLR650 fuel injection project

  • Engine Management System
  • Throttle Body (TB)
  • Fuel Injector
  • Intake Air Temperature Sensor (IAT)
  • Water Temperature Sensor
  • Throttle Position Sensor (TPS)
  • Crank Position Sensor
  • Crank Trigger wheel. (Will modify the rotor to do this function)
  • Cam Position Sensor
  • Coil with internal ignitor
  • Oxygen Sensor
  • Fuel Pump
  • Fuel Pressure Regulator (FPR)
  • Fuel return line to the tank
ECU for KLR650 Fuel Injection Project

G4 + Atom II Engine Control Unit

Choosing an Engine Management System for the KLR650 fuel injection project

A logical choice for a quality and reliable engine management system or engine control unit is the entry level G4 + Atom II. The Atom II comes with an unterminated wiring harness.  It is robust, small, light weight and will be easy to fit somewhere on the KLR.

The G4 Atom supports closed loop operation.

The ECU is waterproof and dust proof. It has an on board  barometric sensor which allows the ECU to compensate automatically for changes in altitude and air pressure density. Therefore there is now no need to re-tune the unit when changing altitude, location or traveling somewhere. The software is intuitive and user friendly and yes for a beginner there is a steep learning curve. Use caution when tuning because it becomes real easy to blow up an engine.



  • 2 x Digital inputs
  • 2 x Temperature inputs
  • 3 x Analog inputs
  • 2 x Trigger inputs


  • 4 x Injection drives
  • 4 x Ignition drivers
  • 4 x Auxiliary outputs*
  • +5V Sensor power supply

* unused ignition drives can be used as auxiliary outputs


  • 1x CAN bus
  • 1 x thirty four pin, waterproof connectors
  • 1x USB tuning connection



  • On-board barometric pressure sensor
  • 32Mb (4 MByte) of logging memory
  • 20 general purpose tables
  • Runs on PC Link software


To get an overview of basic engine management click here

Sensors required for the KLR650 Fuel Injection Project

  1. Intake Air Temperature sensor (IAT) will be installed somewhere in the intake track.  The IAT tells the EMS what the intake air temperature is. The ECU controls fuel and adjust timing based on Air Temperature.
  2. Water temperature sensor (WTS). Tells the EMS what the water temperature is. Based on the feedback of the WTS the EMS can reduce timing and increase fuel to the engine. The EMS controls the cooling fan based on input from it receive from the WTS. Will add a second water temp sensor.
  3. Throttle position sensor (TPS). Tells the ECU what the throttle position is.
  4. Crank Position Sensor.  In combination with the Cam Position Sensor the EMS/ECU determine where in the 720 degree cycle of the four stroke engine the crank shaft is. The current KLR650 crank position sensor will be used
  5. Cam Position Sensor. Tells the EMS/ECU where the cam is in relation to the crank shaft
  6. Oxygen sensor for closed loop operations.

Calculate Fuel Injector Size for the Fuel Injection Project

It is possible for the KLR650 to produce about 80 – 85 HP at the crank.

Use the formula below to calculate injector size at 43 PSI fuel pressure:

fuel injector size formula

The calculated injector size calls for an injector size of 613 cc but to have a bit extra we will use a Denso 550 cc fuel injector and run it at a base fuel pressure  43 PSI.

This arrangement will bring the injector close to initial calculated value.

Throttle body.

A ported cylinder head with 1mm oversize valves will support 410 – 415 CFM.  There is a specific 45 mm BMW motorcycle throttle body available that would be ideal for the job. It is relative small and the design is great. The throttle body is tapered from the inlet to the outlet therefore promoting an increase in airspeed. A BMW motorcycle TPS  will also be used.

Air Box

The air box is one of the major restrictions in increasing the performance of the KLR650 fuel injection project engine. It only supports 282 CFM and will need to be modified drastically.

Because of this restriction it was decided to get rid of the air box all together and and use a K&N air filter.

Fuel Pump and Pressure Regulator

The fuel cell and pump is from a 2012 HONDA SHADOW AERO 750. This setup has an internal fuel pressure regulator in the form of a pressure valve. It therefore allows for a single fuel feed line from the fuel tank. A secondary line vents to atmosphere.

Closed loop and AFR control

An AEM X-Series Inline Wideband Controller is connected to the ECU. It will control closed loop AFR. The oxygen sensor will be installed approximately 30 inches from the exhaust valve.


The battery was moved to the rear of the bike, where it is now installed behind the left luggage rack. This helped to offset the weight of the exhaust muffler and improve the overall balance of the bike.