My son has a 2005 Honda CBR600 F4i. Mileage about 40k.
This spring he parked the bike in front of his house after a working day. Everything with the bike was OK except for a strange behavior when driving on a motorway. All of a sudden the bike would accelerate without doing anything. The bike showed this behavior for some time.
When he wanted to go to work the next morning, the bike wouldn't start. He delivered it in the mechanics shop. He said there was a very low compression on 3 cylinders and no compression at all in number 4 cylinder. He declared the engine dead.

He then brought the bike to my house and I tried to get a compression meter adapter into the sparkplug hole but it didn't work: I could not screw the adapter in because the plug hole is so deep in the engine. I then put some engine oil in all sparkplug holes and now the engine came to life again. And it has done ever since. But the accelerating weirdness is still there.

My son rode the bike to the workshop that had declared it dead. The mechanic said that is was running on only 3 cylinders. My son says it was running like that for a long time. When I listen to a bike with a good 4 cylinder engine it sounds indeed smoother than the Honda. It runs rough as soon as you open the throttle. So I now believe that is indeed running on 3 cylinders. My son might even not have noticed this malfunction.

There is no blinking FI-light.

Now my questions:
- Could it be possible that the 4th cylinder starts working once on the motorway and is the cause of the sudden acceleration?
- How do I determine that a cylinder is not working without a compression or leaktest meter?
- Do I need to pull the engine in order to inspect the valves and cylinders?

Sorry for this long story!
Leo

 

Yes, a 4th cylinder cutting in would cause the bike to accelerate.

Test for a cylinder not working by feeling the exhaust header pipes (carefully), the failing cylinder will be cold(er).

 

Thanks Ed. I will try that.

I also found that the two vacuum hoses from nr.1 and 4, that are attached to the 2 pins on the airbox are not connected. So they are just open. Could this also have anything to do with the sudden accelerating problem?

Still have the question: do I need to remove the engine from the bike in order to pull the cylinder head? Or can it be done with the engine installed?

 

Unfortunately you will have to remove the engine to get the head off.
At 40k the engine should not be dead unless horrendously abused.
The vacuum hoses will affect the running but not sure how much and should have a constant effect not sudden surging.
Why not get a cheap usb boroscope that you can use with your phone, that way you can get a good look at the the in / ex valves and cylinder head without removing the engine c. 20-30 euros.

 

Thanks Al.
The vacuum hoses' only effect was a much smoother idling. Nice!
I will check out the boroscope thing.

In the meantime I have uploaded a video of the sound the bike makes: Please judge the sound, which I think is quite rough. Also in play is a hole in the exhaust pipe. If I hold a cloth over the hole there is less sound but equally rough.


I checked the temps of the exhaust pipes individually with an IR thermometer. Although difficult because a slightly different position gives a big difference in temperature I would say cylinder number 4 is slightly less hot than the others. I estimate 100 F less than the others that were approx. 570 F.

Thanks for looking!
Leo

 

Check them within 10sec of starting the bike - if you have blocked jets that downpipe will remain cold.

 

+1 on the temp at start.
It does sound a little 'fluffy', could be an injector or even a plug / coil stick. The lower temp is indeed symptomatic of a misfire.
Swap over plug see if the misfire follows, then do the same with the coil stick.
If nothing else it will rule out those components and we can start to investigate further.
Do you know if and when the valves were last checked / set as do do tend to tighten with mileage and could cause poor running.

 

I now held my fingers on the downpipes 3 and 4 and started the engine. I could barely feel that pipe 4 heated up later than pipe 3. If sparkplug 4 doesn't fire should it not have been noticeable clearly?
Swapping sparkplugs and coils is what I did already. It made no difference as for the rough running.
I checked the valve clearance myself two months ago: they were up to specs, at least not too tight.

Leo

 

Thanks for the update, you would have noticed if No. 4 plug was not firing.
That should rule them out then, onto the next steps of the fault finding as per the extract from the workshop manual below, do you have a copy?

Points 2 & 3 as they are the easier ones to check, faulty ECM as the last resort unless you can get your hands on one from a mate to help rule out.

 

Thanks Al.
I will check the FPR and injector nr. 4.
Can there be other problems like sticking piston rings or bad valve seating (in nr. 4 cylinder)?