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Thread: Spark plug wires

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    Spark plug wires

    Hi, I'm thinking of replacing my spark plug wires. At this time I'm not thinking of converting my bike to electronic ignition but who knows down the road? Should I replace the caps with 1K or 5K ? Thanks dave

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    Administrator 20774's Avatar
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    Bike model and year? That said, I'd say 5K given that BMW did it beginning in 1977 and continued that when they got into the electronic ignition systems in 1981.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Wires

    Sorry should have said 1971 /5 thanks

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    Registered User Rod Sheridan's Avatar
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    Quote Originally Posted by 79914 View Post
    Sorry should have said 1971 /5 thanks
    Yes, use 5K ohm spark plug caps.............regards, Rod.
    Work is the curse of the riding class

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    Last time I replaced mine, '74 R90, went to auto parts store got some solid core copper plug wire, since that's what was on the bike, put old solid connection plug caps, worked ever since. I thought the older airheads up to the bean can types used regular old copper wire straight through to the plugs? I'm running dual plugs with amplifier and points. FWIW, two whatever.

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    Thanks guys I appreciate it

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    The original caps, long ago, on the earliest of the bikes, was ~1000 ohms. These points driven ignitions worked well, with occasional points area servicing for gap, timing, and lubing the ATU cam and innard shaft. The original coils were such that 1000 or 5000 ohm spark plug caps worked well with the electrical characteristics of the coil, and, lessened spark plug gap erosion. Later models had modified innards of the coils. Several changes, actually, up through 1995 when Production ceased. Some of these changes, such as a thing called capacitance, related to the windings of the secondary in the coil, were changed, to allow a better spark, for better ignition on leaner-running bikes, and the spark is what is commonly called "hotter"; some say Higher Voltage. Along the way were several changes over the years in the primary resistance of the ignition coil (on electronic ignition models), and on some models there was ONE 12 volt twin-tower coil, others retained two 6 volt coils, single towers. These do not operate exactly the same for spark intensity and polarity, etc.
    In the middle was the coils used for the last of the points bikes, when the points were now located in a canister, in 1979-1980 model year bikes. These were the best, over-all, of the points ignition bikes.

    Spark characteristics jumped to much 'hotter' when BMW went to electronic ignition. This type of ignition is sensitive to the spark plug resistor cap value, with values of 1000 ohms being the BAD/WRONG type, which CAN, and DOES, injure the ignition, with the unfortunate nicety of not usually showing up problems until much later, sometimes months later.

    Use of the 5000 ohm caps is proper on models specifying them. For a somewhat marginal bike, perhaps low compression, various deteriorations, etc., if the bike has POINTS, with out without a points booster, you can use 1000 ohm caps, or zero ohms caps. SOMEtimes that will help. Resistor caps and/or resistor plugs, modify the spark. Resistor plugs or resistor caps which are real resistors (not coils) WEAKEN the spark CURRENT, which, in effect, makes the spark 'less hot', while having no effect on the VOLTAGE. Usually this is OK, and serves to weaken radio frequency emissions from the ignition system. In a marginal system/bike, it can make the difference between OK running....and problems.

    DO NOT adjust spark plug gaps AFTER the spark plug has been run, even once....the ground electrode changes its crystalline structure after being heated in the combustion chamber, and in quite rare instances, after being bent during an adjustment AFTER being run, will break off and cause damage. VERY RARE, but has happened. DO NOT use resistor plugs. Many are not really resistors, but chokes, etc. Some use solid wires and resistor plugs. This will work fine, just do NOT use this on the 1980 (1981?) + electronic ignition...those require non-resistor plugs and 5000 ohm caps...NOT SOLID CAPS NOT 1000 OHMS!

    DO NOT overtorque spark plugs. Book values are, IMO, rather a bit high. If you use antiseize on the threads, LOWER the torque value appropriately.

    There are articles on ignition on my website, from simple to nerdy.
    Here is one:
    http://bmwmotorcycletech.info/ignition.htm

    Snowbum

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    Thank you for such a detailed response I greatly appreciate the help and your time, best regards dave

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    Registered User DonTom's Avatar
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    My 1971 BMW R75/5 has a Dyna Ignition, two 6 volt coils in series, dual plugged. IOW, has waste spark, all four plugs fire at the same time, every time.

    When I first purchased the kit, it came with zero ohm wires with zero ohm caps. I thought that was a bit strange.

    What should I be using?

    And I decided to change mine a bit. Instead of having the left coil fire the two left plugs and the right coil fire the two right plugs, I decided to have the left coil fire both top spark pugs and the right fire both bottom plugs.

    So I decided to do a little experment.

    I put the two bottom plugs on an adjustable spark tester so the bottom plugs would not be used during this test, but still have a load.

    I started the engine on the top plugs only and it idles and ran fine (but I didn't try to ride it).

    Then I did the opposite to see if it would run only on the bottom spark plugs. It would start, but would backfire and such and was very flaky. Should it run on the bottom plugs only?

    But then I decided to check the coil HV using my adjustable gap tester from one cap to the other. I then discovered the HV spark is about twice as long on the top plugs than the bottom. But even the bottom has a fairly good spark and I even got a good zap from it at one point. But perhaps a weak right side ignition coil casing it not to run on the bottom plugs?

    Any comments? And what wire and plugs should I be using with such a setup with two plugs in series?

    -Don- Reno, NV
    Original owner of:
    1971 BMW R75/5, 1984 Yamaha Venture
    2002 Suzuki DR200SE, 2013 Triumph Trophy SE

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    Don -

    Of course, Snowbum has a discussion of dual plugging on his website. I think it makes sense to have the alternate setup as you describe...one coil fire top plugs and one coil fire bottom plugs. One reason is if a coil fails, I think you can limp home on just one. The other is that if one coil is trying to provide spark energy to two plugs under compression, that is asking a lot. If you have it the alternate way, a coil is only being asked to fire one plug under compression.

    For an electronic ignition, I think you should be using zero ohm wiring and a 5K ohm cap.

    As for the issue with the bottom plugs, why not try some swapping around and see if you can isolate the problem to a specific component, such as a weak coil.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  11. #11
    Registered User DonTom's Avatar
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    Quote Originally Posted by 20774 View Post
    For an electronic ignition, I think you should be using zero ohm wiring and a 5K ohm cap.
    Can you explain how it could make a noticeable difference, for other than radio interference and such? Anyway, right now, I am using 8MM wires which are around 500 ohms per foot which shouldn't make much difference, AFAIK, in series with a 5k plug cap (total 5.5 K ohm per side). But for now, I am using NE2 caps, the ones that glow with the firing, which will measure infinite resistance on an ohmmeter, but probably drop 70 volts or so from the 15 or 20 KV per plug (or whatever it is).

    Quote Originally Posted by 20774 View Post
    As for the issue with the bottom plugs, why not try some swapping around and see if you can isolate the problem to a specific component, such as a weak coil.
    I was thinking about doing that, but I kinda doubt it will run right on just the bottom, even with the better spark. Look at the intake compared to the position of the top and bottom plugs. The carb looks like it will shoot right into the top plug.

    But I do have a mystery intermittent problem that started before I changed anything:

    From a cold start, engine runs fine, take choke off in a block or so (Mikuni carbs) and all is fine until I ride about a half mile more downhill from this house (I live on top of a hill). Then the engine dies, is difficult to restart, but cranking is fine. Sometimes I then start by compression in 2nd gear, since I am down hill. But it always eventually restarts and then instantly runs perfectly. Sometimes, I am about ready to call for a tow truck but then it starts and runs perfect for the rest of the day, usually. Once in a great while, perhaps once per hundred miles on the average, for a few seconds I will lose power and then it returns to normal.

    Today, I rode it to Lake Tahoe and back, taking a long route through the mountains in the north to get there. Total distance was 142 miles. Just before half way or so, the bike started to miss, loss of power, two different times about a mile apart. Both times was when downhill, but that could just be a coincidence as I have been down hill on much deeper longer grades today with no problem at all.

    I do have a voltmeter on the bike and it runs direct to the hot side of the ignition coil primary. It indicates as normal voltage when the engine dies or losses power. I have recently cleaned the primary coil crossover wire and such too.

    I cannot figure out if this is even an ignition or fuel problem because it doesn't give me enough time to troubleshoot anything before it runs perfectly.

    And ideas of what it could be? I am not sure even what to check between it being a fuel or ignition problem.

    -Don- Reno, NV
    Original owner of:
    1971 BMW R75/5, 1984 Yamaha Venture
    2002 Suzuki DR200SE, 2013 Triumph Trophy SE

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    Don -

    I've pretty much reach the limits of my electrical knowledge! I'm a single plug guy although I do have the Dyna III installed. But I think you're right in that having 5K ohms is better when running an electronic ignition system. This helps to knock down the potential for the radiation of energy which certain can affect other older car radios but can also feed back into your own system...don't want that either. On the higher ohm side, the higher the ohms, the more difficulty the spark energy is going to have jumping the gap. If you have a marginal situation al things considered, then having this "strangle" on the spark is going to create problems. What spark plugs are you running? Hopefully they are zero resistance plugs.

    I haven't retained much about the dual plug situations, but there are some issues with the firing of the plugs, the speed of the flame front, etc., so if the spark is somewhat delayed getting to the bottom plug, the timing could be off now when the plug finally fires relative to the gas in rush and the location of the piston.

    Mr. Snowbum has the only discussion of dual plugging that I'm aware of, although Oak has discussed it in detail in one or more Airmails in the past.

    Tough situation...gas or electrical. Until you have a situation where it's repeatable and you can begin to isolate the factors, I'm not sure what to offer.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    Registered User mneblett's Avatar
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    As I recall from when I dual plugged my R100RT (which ran very well), I used the 1.5 Ohm dual coils from Motorrad Electrik (http://www.motoelekt.com/ignition.htm). Apparently necessary to have a certain amount of resistance to prevent excessive current flow through the electronics/trigger.
    Mark Neblett
    Fairfax, VA
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    Registered User mneblett's Avatar
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    On the stalling problem, next time it happens, crack open the gas cap and listen for a "whosh" from a vacuum in the tank being relieved. One possibility is the tank's vent to atmosphere is plugged or its hose is crimped (the tank vent pipe meets a hose at the bottom of the tank, alongside the rain drain). I do not believe this is likely, but it is something to rule out.

    The symptoms you describe sound like flooding** -- sudden stumble/death, hard to restart. Next time it happens hold the throttle wide open while you crank to see whether it clears/starts faster. If it is flooding, the downhill aspect may not be a coincidence. Have you checked the level of the floats in the float bowl? Have you verified that the chokes (enricheners) are fully shutting after the lever is returned to the "off" position?

    ** if this only happened when the bike was hot, I'd suspect dried out heat transfer paste under the ignition module causing the module to overheat and shut down, but the fact that this happens shortly after starting tends to rule that out.

    On the need for a 5K cap, it suppresses reflection that can send a spike back upstream to roast the electronics. Remember the cardinal rule of electronics -- don't let the magic smoke out!
    Mark Neblett
    Fairfax, VA
    #32806

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    Quote Originally Posted by mneblett View Post
    ** if this only happened when the bike was hot, I'd suspect dried out heat transfer paste under the ignition module causing the module to overheat and shut down, but the fact that this happens shortly after starting tends to rule that out.
    And the fact that the bike is a '71 also rules that out!
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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