Sunday, 8 June 2014

Yamaha YBR 125 Fuel Injection System , FI diagnostics .

This post will be about the fuel injection system on the Yamaha YBR 125 , common faults , test procedures repair and diagnosis .

by the way i just bought the Yamaha FI diagnostics machine , probably not necessary , but who cares it looks interesting to me , i know nothing about it tbh what its capable of or how to use it so should be fun to learn .

The Yamaha YBR 125 has a built in engine managment system , where a series of flashes on the clocks  , engine management light gives out a fault code , find out more here .

Yamaha YBR 125 Fuel Injection System Components

the main components are shown below , ecu , fuel pump (£270) and fuel pipe ( £98) and the fuel injector / throttle position sensor assembly all photoed below .

there are other components obviously like crank position sensor and flywheel ,idle control  , wiring loom differences etc etc . 
a lot of people ask me if a Yamaha YBR 125 carb engine will fit into an injection model frame but it will not
not unless you change the flywheel-stator  at least  , it might then be possible but im not sure yet , i will eventually try but have not had time to attempt yet , may be other differences as well .

yamaha ybr 125 fuel pump injector pump and level sender unit
yamaha ybr 125 fuel pump injector pump and level sender unit

buy fuel pumps from ebay uk here  or Amazon uk here ( be quick they go fast )

or cheaper still the internal pump unit only 

testing the fuel pump it easy , i usually just provide 12v power to terminals and listen to motor if its off the bike ,  this tell you it operates but does not tell you if its proving enough system pressure , i do this with my
tool i made for 2 stroke injection engine bikes i used to work on , ill add a photo later , its basically just a pressure gauge fitted on a T and in the middle of a spare fuel hose i had ( these fuel pipes cost £90ea from yamaha so your brave to cut them up lol . )  , anyway fuel pressure should be 35 psi at idle .

you should hear the fuel pump prime the circuit on intitial turn of the key ,
running thr fuel pump - tank out of fuel can cause damage to the pump .

and testing the resistance values of the fuel level sensor is easy also see below link for expected values
at the empty and full positions .

You can see all the electrical test procedures for the fuel pump and the fuel level sender unit here .      =================================================================

ECU , cannot really be tested unless fitted to a known working bike or swapping it out with a know functioning ECU.
The ECU is located on the frame underneath the tank and is easily removed and refitted to bike .

18 pin fuel injection ecu

Brown - 12Volts
Black/White - 12 Volts
Black - Ground

Red - Magneto Sensor 

Blue - Throttle Body Sensor
Pink/White - Throttle Body Sensor
Black/Blue - Throttle Body Sensor
Brown/White - Throttle Body Sensor

Yellow/Blue - Throttle opening (Variable)

Green/Red - Engine Temperature Sensor
Yellow/Green - Lean Angle Sensor
Orange - Ignition Coil
Yellow/Red - Fast Idle Solenoid
Orange/Black - Fuel Injector
Yellow - Fuel Pump
Blue/Yellow - Rev Counter Pulse
LightGreen - Engine Diagnostic Indicator (Amber Light on Instrument Panel)

White/Black - HeadLight


fuel injector , inlet air pressure sensor and throttle position sensor all can be tested via the
Yamaha Fi diagnostics .

check out the posts on how to test these parts below 

                                     the Throttle body sensor combines TPS , Inlet pressure and
                                     Temperature sensors

Yamaha YBR 125 EFI electronic fuel injection videos , excellent information .


see more Yamaha YBR 125 blog posts 

thanks for reading the Yamaha Owners blog , if you would like to support us you can by  buying your newYamaha YBR 125 off ebay uk here or buying  parts for your yamaha YBR 125 from ebay uk here or you can buy a a Yamaha YBR 125 haynes manual of Amazon UK here or for YBR accessories at Amazon UK here  .


  1. Hi my temperature sensor is not working please give the link or address where i can buy ?

    1. om sorry i dont know , id go to yamaha tbh .

  2. has any one had the issue were the pump dosent prime and the bike wont start after leaving it and shaking the bike it starts to work must be a dodgy connection but in what pump, ecu, any help appreciated

    1. Yeah happens a lot the seals inside pump fail , buy used pump or fix old one .

      it can be hard to get the repaired pump to seal so if unsure buy a used pump .

      it may be the fuel line ( visible leakage )

      or injectors , but usually pump is weaker point .

  3. I own a 2008 ybr custom and i replaced the pump and the pump worked, i then thought it was the fuel injector and i replaced that and then that didnt work so now im kind of lost as it still wont start, i checked the injector terminals and they read at 12.3 ohms which is normal but the bike just wont reach tick over, any help would be appreciated thanks.

    1. what is you fuel pressure ? it needs to be correct otherwise
      bike will not start .

    2. just to make sure you have checked spark ?

  4. I have checked the spark yes but im not sure on the pressure i dont have a way of checking it

  5. Also how can i correct it because i think it is the fuel pressure now that you mention it, completely slipped my mind that it could be that thank you ��

  6. Can the fi system on a 2011 ybr 125 compensate for a 150cc kit. Not on cbt so no problem.