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Imposter Bike, But

Discussion in 'Technical Help' started by Flatty, Oct 15, 2021.

  1. I have a bizarre problem in my daily hack which is a 2012 BMW r1200r.
    It's been raising my hackles a bit starting for a couple of years, but without any serious issues, in that it starts fine, but the battery always seems on the point of giving up.
    (It has of course had a new battery, spark plugs etc)
    The odd thing is, for the past three winters it really doesn't like starting after a petrol fill. Doesn't matter whether premium or regular, which brand or station. The bike has always been ridden for 15-20 mins first, so is well warmed up.
    Petrol fill, and it coughs a couple of times, sounds like the battery is knackered, and then just about kicks into life.
    With this in mind, I had it serviced yesterday, and specifically mentioned the starting problems. They said everything was fine, spark plugs were perfect, etc.
    First cold morning of the winter this morning (felt about five or six degrees), filled with premium. Engine turned over slowly and reluctantly a few times, but just wouldn't start. Battery sounded like it was done (it's only 8 months old and the bike is ridden pretty much daily). Went completely dead, so I pushed it out of the station, let it sit for 15 mins in the low sun, and it started.
    It seems to me to be related to cold petrol.
    Is this a possibility?
    I'm wondering whether to get a new starter motor but it's a really odd thing.
     
  2. Bearing in mind that my expertise is on bikes 40 years old and then some, that sound like a short to me. Leaving aside all the actual components in the ignition/charging circuit, possibly the nearest I ever had to this was the rear of the petrol tank having worn through insulation on the loom.
     
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  3. It'd be intermittent; a little movement and it stops shorting and charges. Shorting at the tank could start after filling up, as it moves with all the extra weight.
     
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  4. Thanks. I'll ask them to recheck.
    I'm convinced in my head that the petrol temp makes a difference, but maybe that is just in my head.
     
  5. I could imagine unlikely scenarios where fuel temp could play a part, but not flattening a near-new battery. Whereas a short could cause all the problems you describe.
     
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  6. Bad earth somewhere?
     
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  7. As a matter of interest, in what scenarios could petrol temp make a difference if you wouldn't mind me asking?? It was fine all summer. First cold morning and night and it rears its head.
     
  8. Oh, just that it would involve contraction so, say a crimped fuel line with marginal flow in warm weather reduces diameter in cold weather.

    Yes, a dodgy earth could cause the same issues. Or an intermittent connection. I'd look for a short first to explain the battery going flat rapidly, but if it's intermittently charging and you've always-on headlights - or lately riding after dark - that could do it.

    Presumably you have a charging light. Assuming that works, once it's running the charging system could be working flat out and balancing a discharge, so the light stays off. When you stop, in certain situations, if it discharges rapidly, starting is difficult. It wouldn't take long to knacker the battery, so it stops holding much of a charge and gets progressively worse.

    Also, rapid discharging would overheat the wire/component; possibly arc, and be a potential fire risk.
     
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  9. Petrol will ignite at any temperature above -23 degrees C.
     
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  10. ...and the fuel in the lines to the injectors doesn't change just because you've filled the tank....
     
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  11. So it might be related to starting a warm-ish engine but with low ambient temperature, rather than the temp of the fuel itself.
    You don't say how many miles it's done, but could it be something like the starter motor brushes worn (so low spring force onto the commutator) or the starter motor cable going high resistance? Lower temperatures would mean a starter drawing more amps. Do either of the cables (starter motor supply or main engine earth) get overly hot during this slow cranking?
    I take it all the other sensors (air temp, water temp) are giving reasonable readings?
     
  12. They are. I think this may well be it. It's done 30000 miles through all weather, hail, rain, snow, ice, salt and occasionally sun.
     
  13. Salt. Lots of salt.
     
  14. This forum is brilliant btw
    Thanks so much everyone.
     
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  15. Flatty, if it was a 916 or especially a 999(they all do it) the advice would be to change the battery power to solenoid, solenoid to starter and main earth cables (We use ExactUk cables to overcome the issue with Ducatis). When the leads are inadequate or failing the high resistance/low cable capacity means the starter draws loads more current from the battery to move and robs the ecu and fuel pump of power making starting a lottery. In the first instance check the leads have properly clean connections and that each of them has a light film of vaseline or similar over the completed connection to stop them corroding once you have done them up. You can also see if the solenoid works OK by shorting the two big terminals (expect a lot of sparks). If the solenoid is dodgy the starter motor will spin quicker when you short the input and outputs.

    On the pump break down due to temperature suggestion, it is more likely to happen when the fuel gets hotter causing failing motors to stop working as effectively due to changes in the winding resistance. Never heard it happening with colder fuel but have experienced it with Lancia (Bosch fuel pump IIRC) on hot days and warm fuel. Took months to diagnose and 10 minutes to fix with a new fuel pump.
     
    #16 Denzil the Ducati, Oct 15, 2021
    Last edited: Oct 15, 2021
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  16. I had a similar problem on my R1150RT, it would start easily from cold but not once warmed up. Was only a problem like you when I fuelled up. I also put it down to a lazy starter but as it would fire up from stone cold I was puzzled, I just learned work around it.

    Final straw came when it did it after a stall on a roundabout on my commute, left the bike for 15 minutes to cool down and it fired up straight away. I ended up changing the battery and the issue disappeared.
     
  17. It's strange, but my hunch is starter motor. I've already tried a new battery.
    Only thing is it does sit for a coupleweeks when I'm away a few times a year without a tender, but that shouldn't really make it behave like this, as you say.
     
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  18. Time for a rebuild on the starter motor…..

     
  19. I'd have a few bits left over.
     
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