Intermittant fault... Engine dies like it runs out of fuel.

[Prof Prolapse]

A shiny penny to the man who can diagnose my Honda CBR 600 FX (1999) - The most reliable and best bikes ever.

The bike runs sweet as a nut, then the revs begin to fall, the throttle becomes unresponsive, and it dies completely over the course of about 20 seconds. It's progressive so not particularly dangerous, and seems more like it has run out of fuel to me. It does this very irregularly though, say four times in 4,000+ miles. But it's just frustrating wondering if it will die.

It's been to what I would consider a good garage and he's just told me he's stumped like me, but has been very good about the bill as a result.

-Alternator, regulator, battery = fine.

-Fuel pump, injectors etc, = fine.

-No vaccuum from aftermarket fuel cap.

-All carb, fuel, air lines checked.

-Valve timing and clearances just done.

-All filters including pre-air are new.

-Exhaust is leaking, and I'm going to balance the carbs after this.

I'm a bit lost here. Fuel and spark seem fine and that's all I know to do. I've ruled out kill switches, side stand switches etc. on the basis that they kill the ignition and this is a slightly drawn out death. My mate has suggested ECU drivers, but I've only seen that on cars and they were a lot more noticeable.

Carbs I know little about in all honesty, but would not have expected to have intermittent faults in combination with running so well. They've been off and the pipes and seals examined, but not taken apart.

This sounds stupid, but I'll say it anyway, it was an absolute fker to get into neutral when it died.

I'm stumped. I can't even throw parts at it!

Edited by Prof Prolapse on Thursday 19th February 14:04

[Prof Prolapse]

RemaL said:

U do have fuel in it?

Yes. :P

bass gt3 said:

Sounds like a form of fuel starvation. Carb'd or injected??
Look for kinks in the fuel lines, maybe a fuel filter in the tank you've missed???

Carbs, that was my first thought. According the Honda manual I have there's only one fuel filter. All lines have been checked. I even had the mechanic inspect the full system today (along with the charging system) to make sure I wasn't being stupid.

rat840771 said:

This maybe a stupid question, but does it die/cut out when the fuel in the tank is at a lower level? I am not sure how these fuel tanks work but if it is gravity fed maybe the feed slows down as the tank get low on fuel?

I'm clutching at straws, there's nothing stupid at this stage I don't think. Tank was about 1/4 full I think, previously has done it half full. Unsure on two occasions prior.

[Prof Prolapse]

I wasn't riding fast, but it wouldn't hurt to read around whether other riders have had similar with carb issues.

I think I will check the kill/sidestand switches as well, seems very unlikely, but it's possible I'm not remembering events as they happened!

[Prof Prolapse]

StuB said:

I had a similar sounding problem.

Mine would feel like it was running out of gas, but what fixed it was the tank breather. The old pipe was not letting air in as I used fuel & it caused starvation, worse from a full tank, as the vacuum builds up quicker.

This was actually my best idea last year, but I was damned if I could find a problem. I discussed this with the mechanic but not sure exactly what he checked in this regard.

I'll check again.

[Prof Prolapse]

Alex@POD said:

You say it happened 4-5 times over a lot of miles, what did you do to restart the bike after it died those other times? Did it restart of its own accord a little while later, or straight away?

I put it in neutral. Then it took between ten and thirty minutes but difficult to remember. As for exactly what I did regarding switches and gears, I am unsure.

What I am sure of though and had forgotten, is when I pushed the start button the lights were on but, no turning over, I don't even recall the click. If the battery and charging system is fine (that is independently confirmed) that means its probably a good idea to assume I'm talking st about it dying slowly and go back the sidestand/kill switch.

[Prof Prolapse]

Right this is my current list (in no particular order);

1) Fuel pump contacts

2) Killswitches/Sidestand switch

3) Breather hoses (again)

4) Fuel pump relay

5) Wiring loom on subframe.

6) Earths (as per 5).

7) Fuel filter (this is actually from late last year but will check all the same).

8) Will fill her up and see if I can make it happen again (before checking hoses) to rule out vacuum.

[Prof Prolapse]

moanthebairns said:

I read this then came back to it so sorry if its been mentioned or sounds stupid but here goes.

Have you drained and cleaned the tank, could it be some crap is swirling around inside that every once and a while finds itself blocking the outlet

Worth a go. I'll check the stopcock whilst I'm doing it.

[Prof Prolapse]

Biker's Nemesis said:

Have you just fitted a new fuel cap.

Yes. But it's done it with this and another two including the OEM one.

I asked the garage to check this and they rang me earlier to say it sealed correctly and wasn't the cause.

[Prof Prolapse]

Andy XRV said:

I had the same problem on my Fireblade and it was the in tank filter, part number 12 below. Assuming it's not broken up it is cleanable.

I didn't realise I had one. I've just been through the honda manual again and still can't find any reference to it.

If the tank is drained and the fuel tap removed it should be easy to find and clean.

[Prof Prolapse]

Biker's Nemesis said:

I would start by checking all pipes, maybe one of them has a kink or one has lost its rigidity and is compressing flat when the tank is in place.

It will be something piss simple, can you hold the tank away from the bike while it is running?

I will do but I'm not sure its that.

I've checked them twice and just refitted them all the other day after doing the clearances. I even checked up all the carb hoses for splits or even the start of them. That was another thing I asked the mechanic to double check.

The biggest ball ache is because it's intermittant. The garage couldn't reproduce the fault, and historically I have done things (like get a new fuel cap) and just have to wait for 4 months before it packs in again.

[Prof Prolapse]

MotorsportTom said:

Nothing useful to add in the way of what it may be but if you use the following website it should have all the exploded diagrams so you'll be able to see if it has what kind of filters where etc.

CMSNL.com

They have Suzuki, Kawasaki, Honda and Yamaha so good for most!

That is incredibly useful. I really could have done with this when I was taking it apart for the valve clearances!

Also shows very clearly I have a filter in the tank. So I'll get that apart.

[Prof Prolapse]

sc0tt said:

PP, What do you need to do to get it going after it has died?

Nothing that I'm aware of. Stuck it in neutral and it kicked over fine.

To be honest mate I don't remember. It's literally a few times over years, it's difficult to recall. It could even be different things given how much has changed on the bike in that time.

[Prof Prolapse]

kiethton said:

Bump to an old topic, having similar issues on my CBR600F 2003 so injected.

Cut out once (first time) on the reserve tank so filled immediately, now doing it every 3 miles or so, always under constant throttle, lowish rev's. Bike feels like it's running out of fuel, starts dieing then flashes the red light and cuts out. I am always able to just hold the clutch in and restart immediately.

Is it likely to be the breather?

Is it an easy thing to access/check?

I think on this occasion mine turned out to be a fuel pump contact which was failing. I speculated it was happy a lot of the time with a vacuum but just every now and again this wasn't enough. I would be very doubtful you have the same set up on your injection CBR.

If you're getting flashing lights however that would be your starting point in a diagnosis? If it's flashing there could be a code somewhere.

Which light is flashing by the way?

Edited by Prof Prolapse on Tuesday 21st February 10:20

[Prof Prolapse]

You have a basic diagnostic system, so it's worth knowing what it covers.

Try and replicate the fault it on it's stand. When it dies re-start with the fuel cap open, see if it helps.

Take the tank off and check the breathers aren't kinked. It should be obvious.

Then I'd be looking at testing the fuel pump, but that's very speculative!

This being a Honda I would be confirming the battery is charging correctly with a voltmeter even if the problem seems unrelated.

Hopefully someone more enlightened can help further.

[Prof Prolapse]

Try what I said then let us know.