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Electrical problem when running hot

Discussion in 'Technical and Troubleshooting Torque' started by ericc123, Dec 12, 2015.

  1. Hi!

    Sorry if I should've been able to find this through search -- I think I'm just not lingo-savvy enough.

    I've got an -86 Suzuki GN250 that runs like an absolute charm in all aspects but this odd one here: when engine runs real hot, typically when cruising at speeds 90+ for a while, it sometimes suddenly starts running choppy. Usually this would go over if I just roll off the throttle for a bit, but a couple of times it's been more problematic.

    Once the engine died on me midst a long day of riding, and when I tired starting the battery was completely drained and starter wouldn't turn. I waited about 15 mins and tried again; the bike started on the little power the battery now had and went on happily.

    Another time, also on a longer trip, it was running real choppy. I stopped, turned it off and then immediately tried starting again; it did, but you could hear that the battery just barely held enough charge to crank the engine.

    – Engine runs great in all other aspects. In city traffic the bike runs flawlessly -- only problematic on long high speed runs
    – Battery holds a charge and the bike eagerly starts after sitting for a couple of weeks
    – All lights etc works fine
    – Problem was there when I bought the bike, and I've done about 2000km without it seeming to get worse.

    I'm suspecting regulator/rectifier overheating? Any ideas? I'm really new to this, so any pointers would be much appreciated!

    Many thanks in advance,
  2. got a little multimeter?
    check voltage at battery when running cold, and then when it gets choppy when hot, pull over and check voltage again.

    makes sense if rec/reg not charging battery when hot, battery runs out, start losing spark..
  3. Many thanks! Since it usually goes back to normal as I back off the throttle it should be fine once i come to a stop.. I'll try hooking up a multimeter that can be read while running and report back.
  4. good plan!

    an alternative to multi is those 10 LED battery voltage kits from jaycar/etc are good.. easy to see at a glance and respond quickly.
  5. Lots of electrical/electronic issues can be heat related. Monitoring the voltage is a good, as an alternative to oldcorollas suggestion I have used these Sparkbright LED monitors before they are a single LED so easy to mount permanently. By the colour and flash pattern they will show under and over charging conditions

    Eclipse Battery Voltage Monitor | SparkBright
    • Like Like x 1
  6. that's nifty and compact!

    if the response time is fast enough to show flickering between green and orange (like when you lose 1/3rd of your field diodes in a car alt) it would be perfect! but for most situations, already perfect :)
  7. The early Hondas have 2 windings on the stator. And that is how the bike acts up. It charges at low RPMS and then dies on the open hyw. I have just found this out with my 1980 CB250RS Honda.
  8. Many thanks for all the help! I'll get the bike out with the multimeter tomorrow, although both those led variants seems perfect I'm just a bit too eager.

    That sounds about right. How would you fix this though? Have stator rewound? And how do you diagnose it?

  9. First things first, make the measurement and then the diagnosis, they were a 3 phase alternator so three windings. There are standard diagnosis steps.
    1. Measure the battery voltage, when the engine is running and then when the problem occurs.
    2. While it is hot and the fault still exists fidconnect the Regulator and measure the AC volts winding to winding with the engine revving 1-2 2-3 3-1

  10. Because I do not uderstand electrical issues very well.
    1/ I started by replacing the spark plug cap and wire to the coil. Didn't fix it.
    2/ Took the CDI unit in to be tested. Didn't Fix it.
    3/ New Coil. Didn't fix it.
    4/ Give up and take it to a motorcycle electrician. The stator is being rewound.
    The battery was always charging while at home. Get it open road and it would die.
  11. So when I was going to get a new battery for my dead multimeter, the bike died on me I city traffic for the first time ever, completely out of juice. I push started a couple of times, and I would run on low revs but refuse to go over 2k. Sounded like it was missing sparks.

    Being unable to find battery for strange multimeter and time running late, I went to the wrecker's and picked up an ugly looking rec/reg for a ridiculous amount of money. When I got back I ran great stationary, but then died on my again as I rode off -- again lacking power to crank the starter.

    Brought the battery home over night for a good charge, got a new multimeter and strapped it on the bike this morning. Now runs fine holding a good 12.4-12.6V running. Perfectly usable as long as headlights are off and signals/break light are used sparingly.

    So i reckon stator here? Should i still try and measure wires coming into rec/reg?

  12. You should be getting close to 14v at about 3,000rpms and if you do not know how to check the 3 wires from the stator. T ake it to the bike shop and it only takes minutes to check. Sound like it could be the stator.
    • Agree Agree x 1
  13. Nah I can check them -- just a bit of a hassle as they're under the tank. Only got 12.6V at the battery when revving though -- with another rec/reg -- so i assume it must be the stator now?
  14. Probably, open the plug that connects the alternator. Switch the multimeter to AC volts and measure the three wires 1-2 2-3 3-1 with the bike revving to about 4000rpm. You should get around 70 volts on each of the measurements.

    What state are you in Eric. If Victoria then Small Coil Rewinds in Geeling can rewind a Stator.
  15. #15 ericc123, Dec 16, 2015
    Last edited: Dec 16, 2015
    Alright -- good news here! I measured the output, and I get between 60-70V two of the wires, while the third gives at best a couple of volts to either of the others.

    The sudden escalation of the problem seems to have come from me trying to take these measurements the other night, only to realise -- after unplugging the rectifier/regulator -- that my multimeter was out of battery. When I disconnected this I also damaged the positive wire coming out of the regulator; it was completely corroded and must have broken off while staying inside of the connector where I couldn't see it. Having reconnected this properly (well, kinda) I now get a perfectly rideable 13.5V at the battery -- with headlights on!

    Thanks for all the help!

    And yes I am in Victoria. Appreciate the tip -- will see if they have time soon. What do you reckon otherwise -- could one of those cheap aftermarket ones from eBay be alright?

    • Like Like x 1
  16. Probably OK, as with all EBAY stuff there is a variability in quality between sellers. The worst that can happen is you will be back in the same situation in a couple of months if the windings on the EBAY one fail
  17. On my Goldwing, I cut the stator plug out (the plug with the three wires from the stator) joined the wires up and shrink wrapped them. You get a lot better conection and moisture cant get in. With the plugs it is hard to know if they have burnt out or not.........So join it and solder it, then shrink wrap.