F650GS Misfire

[Jughead]

I recently had a problem with a client's F650GS, the outcome of which may be of interest to someone.

The symptoms presented were a slight misfire around 15min after starting the motor.  This misfire would get worse and worse, with continuously more throttle needed to keep the bike alive.  However, the motor would ultimately die.

When the bike had cooled, it started up fine again.

I hooked up the GS911, which gave me and error saying that the injector malfunctioned or was shorted to earth.  I checked the wiring for shorts and chafing but found nothing. 

Injector was replaced without resolving the problem.  This led to replacement of the coil and plug cap, spark plug, Voltage regulator, pickup coil, fuel filter, radiator temp sensor, fan switch and BMS (ECU).  All without resolving the problem.

After a month (and ZAR17000) I decided to toss in the towel and return the bike to it's owner.

I parked it in the driveway, started it up to make sure it was still running (as it was when it came to me) and gave it a quick hose down to get rid of the dust.

I then stood waiting for it to die, but after 20 minutes it was still idling happily.  I had to wait for a further 10 minutes for the miss to start, the longest period the motor had ever run.  I suspected it may have bee related to having just washed the bike, so I quickly applied the hose again.  As soon as I did, the miss disappeared.

I then started by trial and error, carefully applying a trickle of water on various areas of the bike when it started missing.

To cut a long story short, after 3 hours I discovered that as soon as I wet the side stand switch the miss disappeared.

On closer inspection, I found that the circlip was missing from the top of the switch and the switch was virtually touching the exhaust.  Opening the switch revealed a very buckled and dirty contact ring.

The ring was straightened, the switch cleaned and replaced with a new circlip.

Problem solved!!!

I then (yes, I know, I should have done it earlier) consulted the wiring diagram and found that the side stand switch is directly connected to the injector and is part of the cutout circuit! 

[kobus]

Did you have a look at the realtime values while the bike was misfiring?

Btw. the side stand/neutral/kill combo switches is part of the cutout circuit on a lot of bikes (R1150s,K series bikes as well), which is why when comms dies we always warn you "Check that: Kill switch is in RUN position, bike is in Neutral, Immo is deactivated".

So a defective kill switch will have more or less the same symptoms if it does not make proper contact.

Thanks for posting this!

[Jughead]

Yes, I did run realtime values.

Only thing of interest was the battery voltage that was spiking up and down, sometimes down to around 3V, in sync with the misfire.  Thus the reason for replacing the VR.

[Haakon]

What Kobus said  !!!  (check the basics first)
I would never think of the "simple" things like that as this occured after the bike warmed up a bit.
Yes, the sidestand switch on the (older?) F650 GS`s WILL fail, sooner or later 
I bypassed mine years ago 

[gregjet]

In defence of Jughead. That was not a Basic fault. No intermittent fault is ever basic and ALWAYS frustrating.