1999 BMW 650 Funduro has very odd symptoms

[Anton Vil]

I have a 1999 BMW 650 Funduro.
A few months ago while riding the bike started to cut out, the same feeling you get when the petrol starts to run out, just before you switch to reserve.

As the “cutting out” would begin, I found that if I switched my lights on, the bike ran smoothly. After a while, I discovered that sometimes the lights being on caused the bike to “cut out” and if I switched the lights off, the bike would run smoothly.

I took the bike in and was advised that the CDI unit was shot. I replaced it and have discovered a new set of circumstances

The bike now starts perfectly, I open the choke, start the bike and let it warm up for a few minutes. When I ride off I must still have the lights on or the “cutting out” starts again.
So, with lights on, I pull away, all is fine until I hit 3000rpm, then the “cutting out” starts.

I change up a gear and all is well as long as I remain under 3000rpm. Once I am in top gear I can run up to about 80km/h at 3000 rpm. If I turn the lights off at this stage it ‘cuts out” again, put the lights on and it’s fine, as long as I keep it at 3000rpm.

If I turn the indicator on when it is over 3000rpm and is “cutting out” the bike runs smoothly when the indicator light is on but “cuts out” when the indicator light is off. So it’s smooth-cutting out-smooth-cutting out, to the timing of the indicator light!

The longer I run, the faster I can go without experiencing “cutting out” after about 10 mins, I can get it up to about 4000rpm and about 100km/h. Lights being turned off at this speed still causes “cutting out”
Once I have stopped and I park ( doesn’t seem to make any difference whether it’s 10 mins or 2 hours ) and I get on to ride again, the bike runs perfectly, not a hint that there is anything wrong at all, can redline it without hassle start to finish, unless I turn the lights off, then it “cuts out” again.
The CDi unit was replaced, I am now stumped as to what this may be. I am hoping that someone could shed some light on this situation.

Regards
Anton

[dieselhead]

Sounds like a voltage regulator issue to me.

A well-known fault with these

See https://faq.f650.com/FAQs/VoltageRectifierFAQ.htm

Ben

[dean36014]

I think I might have a spare regualator kicking around for one of these.

[stinkwheel]

Looks like a fairly universal 3-phase reg/rec on those then.

This being the case, if you are happy with how the wiring works and can decode the wiring diagrams, fitting one off a different bike would be a good plan. A post 2007 R1, R6, fazer 6 or CBR600R one would be favourite.

This is because they use a mosfet voltage regulator rather than a zennor based one. They both do the same thing but they do it in a different way, the mosfet one is WAY less likely to fail.

They will fit and work but you'll need to figure out where to connect the wires. I have a CBR6 one fitted to my VFR.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[hmmmnz]

another vote for reg/rec
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[Fizzer Thou]

https://en.wikipedia.org/wiki/Zener_diode

If you have a multimeter,check to see if all of the earth straps are good.Place one lead onto the negative post of the battery and the other to various chassis or engine mounts around the bike.If there is anything higher than when you connect the two leads directly together then clean up the nearest earth strap connector and cover with something like Vaseline,which will keep corrosion at bay.

While you have the multimeter handy,check to measure the DC voltage across the battery terminals with the lights on/off,indicators on/off etc.Does the DC voltage rise and then stay steady at say 13.5 vdc?If it varies by quite a bit,this variance can cause the fuel injection system to misbehave when lights/indicators etc are being used.
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Just talk bikes.What else is there?

Always have a 'Plan B'