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Thread: resistor plug question

  1. #11
    Senior Member YankeeRon's Avatar
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    Quote Originally Posted by murrayf View Post
    yup no headache answer
    Murry - I see what you mean - my eyes started rolling to the back of my head there for a minute as I tried desperately to understand ...


    Just north of Hartford, CT
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  2. #12
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    just say a few uh-huhs nod your head in agreement

    and grab some resistor plugs
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  3. #13
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    ... ... ...

    I'm not far into my resurrection project, but new plugs were at the top of the list. After I first noticed they were covered in black powder, I noticed they were resistor plugs. Okay, so I pulled apart the caps (having heard about the brass rod mod here) cuz I figured that's what the PO did. Nope. Original resistors still there. So resistor caps and plugs. I guess they wanted to be doubly sure that spark didn't happen early or extra damp (sic). So I put it all back together (no brass rod mod) and used non-resistor plugs.

    One thing I didn't see in the earlier posts... what symptom does the brass rod mod solve? I'm inclined not to fix things that I don't have to...
    Last edited by aprilfool; 03-17-2017 at 07:01 PM.
    81 GL500
    92 Nighthawk 750

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  5. #14
    Senior Member Peter in Cali's Avatar
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    Quote Originally Posted by aprilfool View Post
    ... ... ...


    One thing I didn't see in the earlier posts... what symptom does the brass rod mod solve? I'm inclined not to fix things that I don't have to...
    The resistors fry. Just measure the resistance of your cap. Should be 8 kohms if I remember correctly. Not 2 Mohms. It's not as if they just increase a bit. Then you basically have two spark gaps for the signal to jump - one in your plug, and one in your resistor (or along the outside).
    Peter

    '79 CX500C, low miles

  6. #15
    Super Moderator CXPHREAK's Avatar
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    What Peter said. Though the resisters are 5K ohm, not 8.

    Best gotten rid of if in any doubt over their health.

    Modded caps + resister plug = new resisters every plug change.
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  7. #16
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    Thanks for the info! I just measured about 3k on both. Just the resistor, not the full cap. So for now I'll focus on more broken things...
    81 GL500
    92 Nighthawk 750

  8. #17
    Senior Member Steve1's Avatar
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    The resistors in the plug wire over time may corrode and give a bad spark,these plugs have a built in resistor and will last 100000 miles. I have put them in all my vehicles.https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
    1982 Honda GL500 I SilverWing Interstate " Its not the destination but the journey and Ride Safe "

  9. #18
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    just to stick this bit of reality in here

    here in north america we have this stuff called rain (lol) and bugs like mud daubers

    so what happens to a lot of these bikes is the cylinder plug well drain on the side of the head gets plugged up

    the sparkplug well fills and submerges the plug cap from that point forward corrosion begins on the plain steel spring in

    the cap and on the aluminum rod and on the resistor itsellf so within 24 hrs you already have a rusted spring making the resistance climb

    the resistor is not water proof so it gets soaked with the aluminum corrosion you often see the resistor burnt black

    so when i see a dirty or even rusty looking plug cap i do the brass rod mod
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  10. #19
    Super Moderator Sidecar Bob's Avatar
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    There are 3 places where you can intentionally add resistance in the ignition secondary circuit, the wire, the cap and the plug. If you have resistance in one or two of them the ignition will work well but you shouldn't have resistance in all three. Some of these bikes came with both resistor caps and resistor plugs to meet electrical noise suppression regulations, starting in Canada and with the US regs catching up a couple of years later. Noise suppression was much more important when TV was analogue OTA and people still listened to AM radio. I remember one young hooligan who used to rip up & down our street on his dirt bike, obviously with no resistance in the circuit and absolutely destroying TV reception for the whole neighbourhood. If his noise was reaching TV antennas half a block away you can imagine how many cars' computers could be affected if you were in traffic with no suppression.

    That said, these bikes will function quite well with resistor plugs and resistor caps as long as the resistors in the caps are in good condition
    BTW: I doubt that many cap resistors actually "burn out". It is more likely that the contact points inside the caps become oxidized, stop conducting well and the spark pulse looses power by having to jump the bad contact. In many cases just cleaning everything with contact cleaner and a Scotchbrite will return everything to original function (worked for me).

    Murray's scenario about the parts inside the caps being ruined by flooding makes sense too and since the resistors are not available separately and the aftermarket caps don't have resistors anyway replacing ruined ones with brass rod makes sense when necessary.

    My experience is somewhat limited compared to Murray's but I have personally seen less caps with resistors that don't work than I have with rubber parts that no longer seal (+ problems every time it rains).

    BTW: None of these bikes came with resistor wires. Resistor wires are a really, really bad idea. Instead of having good, reliable copper for the conductor they have basically carbon impregnated string. They may work well when newly installed but after flapping in the wind for a while......
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  11. #20
    Senior Member Technicalfoul's Avatar
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    Its my belief, and hopefully someone smarter than me will correct my thoughts on this, but the reason for the resistor is for impedance matching. The RF noise associated with not using a resistor is because the pulse that creates the spark isn't matched to the electrical circuit its on, and reflects back into the ignition circuit. I think its similar to the same talk that is associated with tailpipe sizing and back pressure. You need to have the correct size pipes or the reflected pressure wave impede the flow of gas out of the tube. If I understand what the smart people on the forum are saying you do best when theres a standing wave is generated that matches the tube diameter and length. Too big is no good, and too small is no good. Same with the electrical wave in the ignition system, too much or too little resistance terminating the circuit and you have problems. In the case of ignition, it mostly will affect nearby cars computers, and AM radio reception, and also a weak spark, as all that energy thats being used to radiate out of the ignition system isn't being used to jump across the spark gap.

    TF
    1983 CX650 Custom


    Search the forum, search the Wiki.
    Its rare that an original problem develops in a 30 year old machine.

    Your question has probably already been answered.

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