Yamaha YBR 125 injector testing .
other posts of interest
Yamaha YBR 125 Fuel Injection System , FI diagnostics
Yamaha YBR 125 Diagnostic Fault codes
I have not had any problems with any injectors i have come across on the YBR 125 , i did once wire one up incorrectly which gave an injector fault but that was my fault .
i have even had customers buy injectors from me after questioning and they were convinced the injector was at fault only for them to bring it back a few days later .
Do yourself and the person your buying parts from a favour and test the components , all the tests you need to do are in the Yamaha YBR 125 Haynes manual so buy one and save money , do not just randomly buy components hoping to guess correctly it rarely works .
you can easily hear the injector firing when the engine is running , or you can check the fault codes -
see out injector fault codes post here .
you can also use the Yamaha FI fuel injection diagnostics machine , which simulates 5 x fires of the
injector to test them , if you have access to one its and excellent tool to own . see our Yamaha FI diagnostics post here .
Testing Yamaha YBR 125 Injector resistance value
I have not seen an actual figure for this but i have got 3 x functioning Yamaha YBR 125 Injectors here
are all test up to 12 ohms .
easy to do set Multi meter to ohms ( auto ) and test between both terminals
 |
| 12.5 ohms |
Since my original 2021 guide, I’ve found that many "injector issues" are actually electrical. Before you buy a replacement or start a messy cleaning process, you should perform an Ohmic Resilience Test. This tells you if the internal solenoid coil is healthy or if it has "Maintenance Debt" that can’t be fixed with a cleaner.
1. The Resistance Test (The "Health" Check)
This is the most important test. You are checking the internal copper winding of the injector.
Set your Multimeter to: 200 Ohms (Ω).
Procedure: Disconnect the electrical plug from the injector. Place your probes on the two metal pins inside the injector's socket.
The Magic Number: A healthy YBR 125 injector should read between 12.0 and 15.0 Ohms at room temperature.
Verdict: * 0.0 – 2.0 Ω: The injector is "Shorted"—it will likely blow a fuse or damage your ECU.
"OL" or 1 (Infinite): The coil is "Open"—it’s dead and will never fire.
15.0+ Ω: The coil is failing or heat-damaged.
2. The Voltage Feed Test
If the injector is healthy, you need to make sure the bike is actually telling it to fire.
Set your Multimeter to: 20V DC.
Procedure: Turn the ignition ON (engine off). Probe the connector pins (the wire side, not the injector side).
The Result: You should see roughly 12V (Battery Voltage) on one of the pins. The ECU "pulses" the ground side to fire the injector, so you are looking for that steady power feed first.
3. Testing for a "Sticky" Injector
Sometimes the electrics are perfect, but the mechanical "pintle" inside is stuck due to E10 fuel gumming.
The Click Test: Use your multimeter's "Continuity" (Beep) mode or a 9V battery to briefly pulse the injector. If you don't hear a sharp, metallic click, the internal spring is stuck.
see video below of entire process
⚠️ SAFETY FIRST: Working with fuel systems is dangerous. Petrol is highly flammable. Always work in a well-ventilated area, away from naked flames or sparks (including heaters). Ensure the engine is cold and wear eye protection—pressurised fuel can spray into your eyes when disconnecting lines.
Revised Blog Post Body:
Since my original 2021 post, many YBR 125 owners have struggled with the shift to E10 fuel in the UK and Europe. The higher ethanol content absorbs moisture, leading to faster gumming and internal corrosion of the injector if the bike sits for more than a few weeks.
If your YBR is hesitating, stalling at lights, or feeling like it’s lost its "Wide Moat" of reliability, it’s time for a deep clean.
Symptoms of a Clogged YBR Injector:
Rough Idle: The bike "hunts" or cuts out when warm.
Bogging: You twist the throttle, but the engine hesitates before accelerating.
Hard Starting: Multiple cranks needed on cold mornings.
Poor Fuel Economy: The ECU over-compensates for a bad spray pattern.
The "Zero-Cost" Test (Before You Dismantle)
Audible Click: With the ignition on, use a long screwdriver as a stethoscope against the injector body while cranking. You should hear a sharp, consistent click-click-click.
Voltage Check: Use a multimeter on the connector. You should see a pulse when cranking.
The 2026 DIY Cleaning Method (Motion Pro Style)
In 2021, we used a lot of "rigged" battery setups. Today, specialized Fuel Injector Maintenance Kits are very cheap on eBay/Amazon and much safer.
Depressurize: Run the engine and pull the fuel pump fuse until it dies.
Removal: Remove the two 8mm bolts holding the fuel rail. Gently pull the injector out (watch for the O-ring!).
The Flush: * Connect your injector to a 9V battery tool or a DIY pulse-button circuit.
Use Aerosol Carb/Injector Cleaner.
Backflush first: Force cleaner through the nozzle end to push dirt out the way it came.
Forward flush: Check the spray pattern. It should be a fine, atomised mist—not a solid stream or "droplets."
Pro-Tips for 2026:
O-Ring Hygiene: If your O-rings are cracked or flat, replace them immediately. A tiny air leak here will cause a permanent "Lean" condition.
Fuel Stabilizer: If you aren't riding your YBR daily, add a stabilizer to combat E10 ethanol damage Don't wait for total failure. A £5 can of cleaner every 5,000 miles is the "margin of safety" your engine deserves.
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