Fuel injector suspected blocked or leaking

The injector is a small electric valve that sprays fuel into the intake. If varnish or dirt partly blocks it, the spray is weak or uneven: the engine runs lean, hesitates, idles roughly and loses power. If it leaks (drips when closed), the engine runs rich, smells of fuel, is hard to start hot, and may flood. Injectors are often blamed for faults elsewhere, so rule out the cheaper causes first: fuel pressure, air leaks and wiring.

Is it safe to ride?

With care, if it runs well enough. If you see or smell fuel outside the injector, do not ride: that is a leak next to a hot engine.

Quick checks first

• Is the engine warning light on, with an injector code?
• Is there a fuel smell or wet spot around the injector?
• Has the bike stood for months with old fuel?
• Does the pump buzz normally at key-on?
• Is the spark plug black and wet (rich) or white (lean)?

Diagnose it step by step

1Is fuel visible on the outside of the injector or its hose joint (key on, engine off)?

• Yes: external leak. Do not ride. Workshop: Check the fuel injector.
• No: go to step 2.

2Is an injector code stored?

• Yes (K-Light 125: P0201 open, P0261 or P0262 shorted): the coil or wiring has a fault. Read engine fault codes, check the connector, then the workshop measures the coil.
• No: go to step 3.

3Does the pump prime normally, and has fuel pressure been checked?

• Weak or silent pump: Check the fuel pump. Low pressure gives the same symptoms as a blocked injector; the K-Light 125 troubleshooting guide checks pressure before the injector.
• Pump fine: go to step 4.

4Do the symptoms point to lean (hesitation, popping, white plug) or rich (fuel smell, black plug, hard hot start)?

• Lean: first find an intake air leak. If there is none, a partly blocked injector is likely. Go to step 5.
• Rich: first check the oxygen sensor is tight and working: Check the oxygen sensor. The K-Light 125 manual says an O2 reading that stays above 500 mV when warm suggests a leaking injector. The K-Light 125 no-start chart also lists injector overflow for a wet plug.
• Use Read a spark plug to help decide.

5Has the bike stood with old fuel, or had dirty fuel?

• Yes: drain the old fuel, fill with fresh fuel and ride a full tank. Mild varnish sometimes clears. If not, go to step 6.

6. Workshop injector service. The workshop checks the coil resistance (K-Light 125: about 10 Ω), cleans the injector in an ultrasonic cleaner, tests its spray and leakage, and refits it with new O-rings. A leaking or failed injector is replaced with one of the same part number. See Check the fuel injector.

Causes, most likely first