I own a 2011 Honda CBR 250r MC41 which was sitting idle for a couple of weeks, if started flawlessly except it won't idle at 1.5K and died after a few seconds. So, I tightened loose air box hose clamp fired it again still won't idle. I thought there must be some blockage in fuel line. Hence, I sprayed little WD40 in the fuel line. Since then the bike didn't start.

I've changed the spark plug, cleaned the fuel injector, cleaned fuel line still the bike won't start.

Update: The plug sparks and looks like this .

Update: Testing for spark.

  • How did you clean the fuel injector?
    – HandyHowie
    Commented Mar 30, 2023 at 8:46
  • Well, I've cleaned the fuel injector using a method similar to this; except I've used a syringe for sealing the fuel injector.
    – Caesar
    Commented Mar 30, 2023 at 9:28
  • The plug doesn't look as though it has fired at all. It also looks dry. This would tend towards there being a fueling issue, but testing the spark would be an easy start to diagnosing the issue. Commented Mar 30, 2023 at 18:49
  • The new plug sparks. But, should it be this dry?
    – Caesar
    Commented Mar 31, 2023 at 7:36
  • 1
    What would make you think WD40 would address that any better than fuel does? WD40 is a jack-of-all-trades master-of-none, not particularly good at any task except polishing missiles (for which it had 40 iterations). It is, however, very good at degrading plastic and rubber things. Commented Mar 31, 2023 at 23:24

1 Answer 1


Things to check in a situation like this -

  1. Remove the spark plug and check that there is a spark.
  2. Check that the fuel pump is running
  3. Check the fuel pressure
  4. Check that fuel is getting to the cylinder (spark plug wet with fuel)
  5. Check that fuel comes out of the injector
  • Quick question: How do I check if fuel comes out of the injector?
    – Caesar
    Commented Mar 31, 2023 at 14:33
  • It may be possible to remove the injector and keep it connected to the fuel rail. Turning the engine over should then make the injector spray fuel. If you do this however, you should do it very briefly. You will also need to be very careful that the ignition is disabled and that there are no other sources of ignition, or you could end up with a fire on your hands.
    – HandyHowie
    Commented Mar 31, 2023 at 16:46
  • Alright, checked the injector it's spraying fuel.
    – Caesar
    Commented Apr 1, 2023 at 11:18
  • If you have a spark and fuel being injected, then the only thing left is that they are not happening at the right time. Have you done anything to change the ignition timing? Presumably you can tell that you have compression too?
    – HandyHowie
    Commented Apr 1, 2023 at 11:42
  • I did a valve clearance check recently, one exhaust valve was tight by 0.12mm. Could this cause starting issues?
    – Caesar
    Commented Apr 2, 2023 at 11:27

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