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Electrical problem

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  • Electrical problem

    I'm back for the week for spring break and have decided it's almost warm enough to ride, so I might as well get the thing running.

    Here's the situation so far:
    The bike starts and can be coerced to idle when cold but not well and when it's warmed up it will not idle at all. When idling it sounds as if only a few cylinders are firing, then you can hear more cylinders fire and the revs go up but then they stop and it idles lower than 1K.

    I have taken the carbs apart, they were quite clean but I thoroughly scrubbed them up anyway. The Battery has been on a trickle charger inside for the winter and the tank and carbs were empty and inside as well.

    I recently figured it might be an electrical problem. The battery, partially drained, read 12.6 volts, just fine. however when idling it reads upper 13s and when revved it jumps up to 15+ volts. I figure this is a bad regulator/rectifier, which is nestled in the alternator. First question, can I just replace the reg./rectifier or would it be cheaper to just get an entire alternator assembly, I found alternators on ebay for ~$40 shipped but not seperate reg./rectifiers.

    Next I looked at ignition. The plugs look fine so I tried the "put the plug against the engine block and hit the starter" test and saw a weak yellow spark from all cylinders. This lead me to test the ignition coils. They read 1.6 and 2.6 ohms where the clymer manual says it should be 3-5 ohms, and across the plug wires there is infinite resistance where it should be 25,000-45,000 ohms. I was suprised that it could be infinite and still spark.

    I figure the ignition coils may have been fried by the high voltage from the alternator, but I'm wondering, should I replace the coils (fairly expensive) and the alternator, or should I do one at a time to see if the problem gets fixed by the alternator? and where is the best place to buy used parts? Isn't SpecialK into that?

    Oh, almost forgot to add, is there anything else I should check, electrically, that may have been fried, anything that's sensitive to that kind of stuff?

    Thanks a lot for the help,


  • #2
    (A) How old is the battery? Is it maint-free or standard? Which brand and model?
    (B) Have you checked the water/electrolyte levels on the battery?
    (C) Does it idle any better if you disconnect the headlight, and/or if you swap to a known-good/new battery?

    I ask all this because different brands produce different amounts of CCA's, and if the water is low (or the electrolyte weak), you can still occasionally get the right voltage but insufficient amperage (esp. if one or more of the cells is dry or calcified/mineralized).

    16 year old bike. Hmmm...
    Voltage should be 12.8 with the key off, battery fully charged.
    Voltage should be 14.7 (14.4 - 14.9) with the engine at 5k RPM if it has a good, fully charged battery. If it's going into the 15's, I'd suspect the battery first, the rectifier pack second. Alternators rarely fail on Kats.

    As for the coils, they don't go bad by over-voltage, only by heat, age, cracking and/or vibration (the oil inside breaks down/leaks out and stops acting as a proper heat sink, or the wire coils form a shorter path by losing their insulation). Retest the coils -- once cold, and then again after blowing them with a hair dryer for two to five minutes to heat them up to 180 degrees (F). If they fail at that point, replace and retest again. If the coils pass, I'd probably go buy a maint-free battery and start tracking down a cheap rectifier pack...

    Good Luck!
    =-= The CyberPoet
    Remember The CyberPoet