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  1. #1

    Join Date
    Jun 2014

    Default 83 Vt500 Coil Testing

    Okay, so the new project is being a bit moody.. by being a bit moody, i mean being a down right bi*$#!

    I went through carbs, found a small hole in top of diaghragm, made repair for temporary purposes. Rest of carb looked good after extensive cleaning.
    New plugs, New 12v, 175 CCA lawn mower battery.
    The bike cranks fine the first time, backfires when idling and lingers in high rpms before coming down from a rev. I'm sure these are carb being out of tune especially after I took the airbox off and have foam clamped down at the end of the plastic neck that use to connect carbs to airbox. So I plan on rejetting and tuning but that's not the issue.
    After a bit of riding around the yard, when you shut the bike down she will not crank back up. She will turn over, but not fire.
    I am getting spark, I have tried opening gas cap, it's not vapor lock.
    So I decided to test the coils with a multimeter.
    here's what I got
    When i connect A and B, it bounces for a few seconds. Watching it the numbers will show, 42, 13, 73, 24, before settling on a nice 3.2. I tried it many times and sometimes it would just go from 4.0 to 3.2 and then settle. I had coils on table so i was testing everything straight at the coil.
    Then I tried combinations of A with C or D, and B with C or D and had no reading what so ever. I also tried C and D with a ground to the frame, and still nothing. If im not mistaken I should be getting 6,000-12,500 here. I also connected one plug wire on the coils and tried A and B with the other end on the end of the plug wire and got no reading. I would say that their bad and chunk them but I know I'm getting spark. I put them back on the bike and she fired right up.
    So am I not testing something correctly?
    Could the carb being so badly out of whack hold a influence on not cranking when warm.

    Ah yes, I also tested the charging system, at idle my battery had 12.70 volts, the same at 2500 RPM, and 13.00 volts at 5,000 RPM. So in my head, I'm charging correctly.

    Click image for larger version. 

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    This is the end of my air intake system. Or beginning, however you wish to look at it.
    Click image for larger version. 

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    Last edited by Hotel; 07-08-2014 at 1:04 PM. Reason: typo

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