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erratic engine when lights on

Discussion in 'Technical and Troubleshooting Torque' started by Devery, Mar 15, 2010.

  1. This problem I've been having with my engine missing a beat every now and again and behaving erratically hasn't gone away like I thought. The problem now only exists when the lights are on. So it is electrical. But why only when the lights are on? Could it be a connection shorting that is part of the lighting system?

    Here is a wiring diagram;

    Any ideas where to look to try and solve this one?

  2. I had a similar problem and it may be a long shot but check your battery terminals for a loose earth first before you go any further.
  3. If checking your ground points (on the battery and any on the frame) doesn't fix it, it might be time to pull out the old multimeter and check the health of your electrical system. Your symptoms don't scream charging issues, but it pretty easy to check before you go on a serious wiring inspection.

    This is easier if you have a helper, but you can do it solo. I would start by checking what sort of voltage your battery is putting out with the bike off. Then start her up and check without the lights on at idle, and again with the lights on at idle. Bring the bike up about a 3rd of the way through the rev range (in neutral of course) and again check the voltage first without the lights then with the lights on.

    What you want to see is those last two readings being about the same - if they are not we are possibly looking at a charging issue (or maybe a buggered battery). You are also wanting all 3 sets of readings to be in the expected range for your bike - assuming a standard 12v battery, at rest with everything off you want to see a reading of 12.5 volts to 13 volts (or there abouts - indicates the battery is at 75% charge or more and is happy).

    At a 3rd of the rev range you should get a reading above 14 volts (probably somewhere between 14 and 14.8 volts). If so, that's good, everything is charging nicely. At idle, it should be somewhere in-between (typically mid 13 volts, but older, smaller capacity bikes tend to put out less) - I would also expect the lights to make a bit of a dent in your readings at idle - they shouldn't once you have reved up.

    If all the readings are fine, sadly you are going to have to dig deeper into your wiring - check along to see if there is any corrosion, loose connections, damaged or cracked wires, and so forth. Hopefully it will be something silly and easy to fix.
  4. Wot he said^.
  5. Thanks for that. I will do the tests tomorrow.

    What is puzzling me is the fact that it is only happening with the lights on. If the battery isn't charging so well with the lights on could this cause the bike to behave erratically?

    Lets hope so!
  6. Toasted rec/regs do all sorts of strange things - an unhappy rec/reg can not only screw you battery over, but every now and then the now unstable power supply can fry/melt things (connectors love to melt and introduce pesky little short circuts). Your stator could on the fritz, which has caused you rec/reg to go nuts, and the problem has spread - but we are getting ahead of ourselves. Testing the overall health of your electrics (and charging system) is so straight forward there is no good reason not to do it!
  7. Most bikes are barely charging at idle. With the lights on your bike may be seeing a slight discharge. So you may be seeing a minor net loss of charge at idle.

    Also putting the lights on puts the engine under slight load.

    Does it miss a beat at idle or at higher revs? At standstill or whilst riding?