Bike cuts out after 40 seconds at idle - advice sought

[Barny]

Hi All, I'm very much hoping someone will recognise my symptoms or be able to give me some pointers. 

 

So I've got a 1999 VFR800Fi (in glorious yellow!) and I've had it about 6 years. It ran fine last year, but I do very few miles on it currently. When I took it out a few months ago, it would run, but then cut out on idle. Also, when I came off the power, there was a lot of engine braking and when I got slow enough, the engine would cut. 

 

This last weekend, I :

• Pulled out the rear plugs - they looked ok and the gap was within tolerance, although I've not changed them in my ownership. 
• Sat the Battery on charge
• Put fresh petrol in (I"m in the UK and standard fuel is E10 these days

 

Still no dice. So I drained the tank, pulled it off and found: 

• A Sticker on the airbox that said I had a K&N filter installed
• A Bloody mouse nest!  https://photos.app.goo.gl/j1mi4zUVKYQoQoi18

So I threw the nest away, cleaned out the air filter in soapy water (twice) and re-oiled it with ATF, because I didn't have a K&N Service kit. 
 

After re-assembly, I fired her up and she ran! However, after about a minute, the revs started to waver and eventually it cut. If I waited and re-started, I got the same again, about 40-60 seconds of idling, getting more uneven and hunting, then a cut. If I hold 3k on the throttle, the bike cuts a bit sooner. 

 

When I turn on the ignition, I hear the fuel pump run for about 3 seconds, then stop. I've noticed that if I run the bike till it dies, then immediately power off then on, to get the pump run for another 3 seconds, then I'll get another 40 seconds of runtime. 

 

Battery reads about 12.6 currently. Voltage when running is 13.8 at idle, falling to 13.5 at about 5k. It's got an Electrex-World aftermarket regulator fitted. The voltage doesn't seem to fall any further when the bike starts to fail. 

 

I'm slightly at a loss as to what to look at next. It sounds possibly like Fuel Pressure regulator related? Either that or the fuel pump runs at start, then not again for some reason? 

 

Any advice on what to look at or what to try next wold be greatly appreciated. 

 

Barny
 

[Bren]

Your voltage falling to 13.5 is the first suspect. Generally at 5000rpm with a good charging system you should have 14.4 ish. Get a FH020AA from a cbr500 or Yamaha and fit that, that'll fix your charging for a start.

But why your engine only runs for short periods, that shouldn't have anything to do with the rectifier at that point because it's going off battery power anyway. 

Sounds like a fuel pump problem or pump power issue. It's not getting power to keep running. Did you check the fuse?

3 seconds or so priming is normal.

[Barny]

Thanks for replying @Bren !

 

I'll get the fairings off tomorrow and check all fuses and relays. I did think as well if I can get at the wiring, I'll put an LED/Resistor in parallel with the fuel pump, so I can verify it's powered once the bike is running. Looking at the wiring diagram, the ECU is controlling the pump through the fuel cut relay. If I can prove to myself that the pump is running whilst the engine is running, that'll hopefully eliminate one source of problems. 

 

Points taken on board about the reg/reg - I would have expected a higher reading whilst it was running. I'd also expect that'd still be enough voltage to keep things running - I could try running it with jump leads hooked onto a running car, so I'd have 14-ish volts available - I'd expect that not to help here, but it might be a simple enough test to run. 

 

The tank appears spotless and the bike only has 30k miles on it, so I'm not currently suspecting fuel filter. 

 

Thanks

 

Barny

[Bren]

You would have enough power to keep it running with what you've got, the rectifier change is something for later.

It just sounds like it's not getting fuel to me, or air. Would the ATF you sprayed the K&N be too thick and restricting air?

You may have a kinked fuel hose from the tank that won't allow enough fuel to flow. As you just lifted the tank to get at the air filter this could have happened.

Good luck with it.

[Barny]

I'm beginning to think you could be right with kinked fuel hoses! I left the bike on charge last night. Just now I lifted the tank, disconnected the fuel pump and ran a couple of wires into the back of the connector and hooked that up to a multimeter. 

As I turned on the ignition, I got 3 seconds of 12v, followed by 0. On starting the bike, I got wildly fluctuating voltages - between 5 and 12, for about 10 seconds, then it settled down to 13.8 at idle, which is what the regulator puts out at idle. 

This was tested with the tank propped up at the front - I didn't even think to put it back down. 

The bike then idled just fine for 5 minutes straight. I was able to blip the throttle and the response was crisp  - it had no issues holding 5k either. 

 

So, it seems worth carefully re-assembling and trying out a cautious road ride. I'm not sure about the fluctuating voltage on the fuel pump line - the pump ought to be either on or off, as it's relay controlled. That might be an indication that the fuel pump relay (or the connections to it) has issues. 

I might go investigate the wiring to the relays before I venture out onto the road. 

 

I'll report back on progress

 

Barny

[Grum]

How old is the battery and what brand?

Charge the battery then take it to any good  Automotive parts store and have it Load Tested.

Any doubts about the Fuel Pump Relay, for testing purposes you could swap it with the Hi Beam Relay.