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Confused checking coil resistance using Honda Manual

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  • Confused checking coil resistance using Honda Manual

    The top drawing is easy to understand and to measure.
    I'm confused by the bottom picture. I have 0 continuity between the two front spark plug boots (and none between the rear plug boots).
    I've even put in spare spare spark plugs into the boots and tried to see if there is any continuity between them, assuming I wasn't getting the probe onto the spark plug holder correctly, and zero continuity and no k Ohm reading whatsoever.
    Or am I supposed to measure between the plug boot metal and the ignition coil supplying it? It's time like this I wished I had the native Japanese version of the manual.
    I still haven't found the rear ignition coil yet, either.
    Hawk with many differently shaped fuel tanks.

  • #2
    I think you're doing it right - measuring the resistance from one spark plug boot, through the coil, to the other spark plug boot. If there is actually 0 continuity, either the circuit is open (i.e. something is broken), or the resistance is too high for your multimeter to measure. A few things to try:
    1. (disregard - I just reread your post and saw you were making sure your probes contacted the metal part inside the boot)
    2. make sure your multimeter is set to the correct range (I make this mistake way too often with my multimeter - the display only goes up to 4000, so if something is 5000 ohms, for example, I have to change the range from ohms to k-ohms to be able to read it.)
    3. check your wires and boots separately to make sure there isn't an actual open in the circuit.

    The rear ignition coil is mounted to the rear of the frame on the right side. Here's the best picture I could get...
    Rear Coil.jpeg

    You should be able to get to it if you remove the right side rearset.

    Good luck!
    Last edited by cjb762; 09-05-2021, 11:49 PM.


    • #3
      i don't believe the manual calls for the testing you're doing, plug cap to plug cap, and it means nothing. bit i might be wrong as i don't have the manual............
      Last edited by squirrelman; 09-06-2021, 11:28 PM.
      "It's only getting worse."

      MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

      Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.


      • #4
        I completely removed both coils/plug wires from the bike.
        The resistance of the spade terminals on both coils are correct at about 3 Ohms. I have a cheapie tester, so I allow some tolerance.
        No matter what setting I do on tester resistance, neither coil has any continuity whatsoever between the two spark plug terminals inside the body on either the coil leads themselves or when connected to the spark plug wires. This is the 2nd picture at the bottom of the Honda Manual.
        All 4 plug wires (just the wires when removed individually) when completely disconnected read about 5K Ohms, so the wires have some resistance.
        This 30-36K or 25K Ohm readings for the "secondary coils" referenced in the Honda Manual absolutely don't match anything on either of my coils. Touching every possible connection point in every possible permutation, using every possible resistance setting on my tester comes up with zero, zilch, nada, donut, nothing even close. 0% continuity for everything other than the spade connectors.
        I've used dielectric grease and all the parts are in great cosmetic condition.
        I find it unlikely both coils would fail in the exact same way at the exact same time.
        But I'm still having terrible carburetion from 3000 to 6500 rpm. It idles mostly fine and at 6500 rpm it clears out and runs fine. It doesn't start easily. I think I've literally gone through every possible thing, from replacing all the jets, to using a spare carb, to re-measuring the valve clearance 4 times. Plenty of fuel through a new filter, new air filter, completely rebuilt and reassembled (6 times now) carbs. I'm at my wit's end.
        Hawk with many differently shaped fuel tanks.


        • #5
          That's strange. I'd be surprised if your coils were actually bad though, considering you bike runs - and I agree that it would be unlikely that both coils would fail like that. Not impossible though. That said, one of the many, many people on here who are significantly smarter than me about Hawk engines is sure to pop up soon.

          Also, here's a video on coil testing, just to confirm you're doing it right - which it sounds like you are (skip to 1:40 for the primary coil test, and 2:14 for the secondary coil test)...

          Last edited by cjb762; 09-06-2021, 12:51 AM.


          • #6
            Thank you for the video--it confirms everything I was doing. I've even tried doing it with the spark plug wires removed from the coil. At 5:00 he says it's fine if the secondaries don't have continuity with the primaries on certain bikes---but Honda specifically calls out the resistance as shown at 2:20 to be 20 to 25kΩ, I think I'll try measuring someone else's coil and see if there is any difference and whether it's my multi-meter that's at fault.
            Hawk with many differently shaped fuel tanks.


            • #7
              Yeah - I don't think there should be any continuity between the primaries and secondaries on our coils. They are two separate coils with no "mechanical" connection. Electricity for the spark is transferred from the primary to the secondary coil through induction. The only relevant measurements are of the two coils separately (primary coil being measure through the spade terminals, and secondary coil being measured through the spark plug boots and wires.).

              Also, the 20-25kΩ measurement is only if you are measuring the secondary coil directly at the terminal without boots or wires. Since the boots have resistors in them, the measurement through the boots should be 30-36 kΩ.

              Here's a picture of mine. Note the resistance is lower than Honda specifies, because I am missing one of the boots...

              Coil Test.jpeg


              • #8
                Nice Klein multimeter--you're serious about measuring electricity! I still get only OL on every possible resistance setting. I've done it with both spark boots on and both boots off, too. Hopefully local "Chuck" has a coil or two I can compare with and absolutely confirm my cheapie multimeter is bad or whether there really is an issue. Chuck races them for years and mentioned a week ago that he's never, ever seen a stock Hawk coil go bad, even in race bikes.
                On my rear coil there is a C-shaped clip with holes in it that slides over the mounting lug metal (the mounting bolts go through them)--and they've come off. My front doesn't have them (and I've never removed the coils in 10 years, even when they worked correctly). Probably no real function to it, but I thought I'd mention it.
                Hawk with many differently shaped fuel tanks.


                • #9
                  I do like to measure electricity.

                  I think it was only about $35 when I got it on sale at Home Depot...

                  You are having a very strange issue there though. I'm sure Chuck will get you sorted out!

                  As for the c-shaped clip (30520-ML7-000 "spacer') ... the parts fiche only shows that for rear coil - so I think you're good.


                  • #10
                    Of course when I show someone else how mine don't work, they both magically work for the first time exactly in the center of normal at 32.5kΩ. I'm performing the test absolutely the exact same as before, too.

                    So absolutely every testable electric resistance and voltage is fine at every connector.

                    I'll button it all up again and see if anything changed. If not, next step for my terrible carburetion is putting my carb on a known working Hawk.
                    Hawk with many differently shaped fuel tanks.


                    • #11
                      If I had a nickel for every time that happened with one of our cars.... It's almost as if our cars and bikes are screwing with us.