Hi all, I fitted a new battery to my 748 in March, rode the bike a few times in April and haven't fired her up since then. I came to ride it yesterday and the battery was totally flat. Odd since it has no alarm. I put the (Oxford) trickle charger on for a couple of hours, but there was still not enough guts to get the bike started, so I bump started it and off I went. The bike was running very rough, but I have had this before when the battery has been a bit flat, and it has recovered over 30 minutes or so. Having ridden for about 40 minutes, I figured that would have been more than enough time to get the batter charged up - so I stopped at a petrol station, and....how wrong I was! Still no life at all (couldn't even hear the fuel pump when I turned the ignition on). If the alternator had gone I wouldn't have been able to ride it at all - but my main question is, why is it so rough? Interestingly, when I put the lights on or touch the brake, the bike suddenly picks up and runs really smoothly....I guess it's something to do with load on the alternator and a battery fuelling compensation but really sure. Thanks Jonny
This means that the fuel will be a minimum of 5 months old? This is the first place to start for sure!!!! also get a full charge on the battery and make sure all major 'load' connectors are clean and not rusted up. Further from that, new plugs and clean the fuel filter out in the tank.
Yes it has a full fresh tank in now but made bugger all difference - I am curious about the fact that the running improved significantly when I put the headlights (or any other light) on. It would be running rough, but if I pulled the brake on enough to activate the light but not actually engage the brakes it would suddenly be smooth. I have had this issue previously on another bike a few years ago but can't remember what the resolution/reason was.
Reg/rec seems to be a good place to start, measure at idle running and then rev the bike, some have reported voltages of 18/19 when the reg/rec goes.
As already said my first check would be the charging system first, I have just had a reg/rec go on my 748 it was over charging 16v at tick-over. Check all respective connections particularly the ones from the generator to the rec. It does seem odd that the bike runs smoother with the lights on if it was under charging and your battery was running down it would start spluttering and get worse within a very short time. Steve
That'll be me, it melted a hole in the bottom of the battery case, funny thing is the bike worked perfectly at 19v and the only clue to the regs demise whilst being driven was a slightly eggy smell from the battery as it turned out. My money is on the main ignition relay (the yellow 40A one by the battery) although odd faults like this where it intermittently clears are more often than not an earth connection breaking down. Can you check the voltage on the charger? I have an Oxford one which "works" but has incorrectly set trigger/control voltage points on the bike setting so the trickle charger is useless. It only charges up to 12.7v and the battery needs to get down to 12.4v before it will bulk charge. To get the battery fully charged it needs to go up to around 14v and bulk charge from 12.6v.
This is why I don't use a fancy lightweight battery on the 916 - it needs the Ooomph, both to start and keep it going, especially if it's not used everyday. Li-ion batteries have their place but not on an old Desmoquattro...
Had the exact same problem, my reg was outputing 19v, seemed that when indicators were on with my bike It reduced the voltage enough to stop upsetting the ecu so It ran properly. As Birdie and Denzil have already pointed out you need to put a multimeter across battery to measure the charge output. Darren.
