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Thread: Spark Plug Cap Mod

  1. #1
    apriliaforum Member
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    Spark Plug Cap Mod

    I suspect that a contributor to the Pegaso's harder starting, increased stalling, sensitivity to carburetor tuning and lower fuel economy than the F650 has something to do with the ignition. The large cylinder diameter leads itself to the need for a strong spark. There must be a reason that BMW expended the effort and cost for dual spark on the carbureted F650 and then again on the later fuel injected F650GS. The F650 Funduro gets better fuel economy despite larger carb jetting (41.3 pilot vs our 37.5, 140 mains vs our 110/112.5) plus enabling owners to start a cold bike and immediately removing the choke.

    Per the service manual, the Pegaso ignition coil should have 6-12kOhm resistance when measured without the cap.
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    The Beru spark plug cap adds 1kOhm on top of the coil's resistance for a total acceptable coil-to-cap resistance range of 7-13kOhm. The Beru cap is very nice quality with its heat shield and seal but there is one weakness; the internal resistor. Over time, this resistor gradually starts to breakdown and increase in resistance. It is a gradual process that seldomly completely fails, making diagnosis difficult.
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    Earlier Pegasos called for non-resistor spark plugs as all the resiatnce needed to protect the CDI was built into the cap. As more electronics like GPS and Intercomms became popular, Aprilia changed to a NGK "R" resistor spark plug which adds another 5kOhms to further reduce interferrence. But they never changed the cap back to a non-resistor. You only need to have resistance in plug or the cap, not both because combined can result in too much impedance (per NGK). My feeling is that the large cylinder of our thumpers coupled with a single, overly impeded spark and you get the finicky bikes many of us struggle with, especially when the carbs are less the perfect. Time to remove the Beru Cap resistor.

    I started by removing my coil and checking the resistance, which should be between 7-13kOhms. I struggled to get a good reading due to some corrosion of the brass contacts inside the cap. The best I measure was 10.07kOhm, though mostly the numbers were in the 12 MOhm range. I knew something was bad.
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    Last edited by andysrage; 02-01-2013 at 06:26 PM.
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  2. #2
    apriliaforum Member
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    The spark plug contact inside had some corrosion. Fortunately, these caps are rebuildable.
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    Start disassembling the cap by unscrewing the spark plug contact with a flat blade screwdriver.
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    Once loose, use a spark plug contact still does not fall out of the cap. This is due to a wire clip on the contact that holds onto the threaded spark plug post. Use a spark plug to "grab" the contact and pull it out. Following it will be a resistor (red cylinder with brass ends), a small aluminum slug and a brass spring.
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    Last edited by andysrage; 02-01-2013 at 06:02 PM.
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  3. #3
    apriliaforum Member
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    Here is the resistor measurement from my brother's cap: 1.1kOhms
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    Mine had the brass ends corroded. Even after some cleaning, I could not get a repeat as good as my first, fully assembled resistance reading. It was measuring 14.3MOhms. That's 1400 times more resistance than it should have! Definitely signs that the resistor was on it's way out.
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    Last edited by andysrage; 02-01-2013 at 05:58 PM. Reason: Poor math
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  4. #4
    apriliaforum Member
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    I measured the length of the resistor and aluminum slug to be 1.447 inches (36.75mm).
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    The diameter was .176 inches (4.5mm).
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    The recess in the spark plug contact was larger than 4.5mm so I made a cylinder to match the length of the resistor and aluminum slug from .188inch brass rod.
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    Last edited by andysrage; 02-01-2013 at 05:55 PM.
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  5. #5
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    After cleaning the Spark plug contact and brass spring, I reassembled with the brass rod replacing the resistor and aluminum slug. I applied a tiny amount of dialectric grease between the components to prevent corrosion in the future. End result: 8.6kOhms total.
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    I'll be matching this with an NGK Iridium DR8EIX spark plug.
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  6. #6
    apriliaforum prov-nov
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    Very interesting

    Good idea - on my Peg there is a red NGK spark plug cap/cable.
    I will try to measure the resistance of it this weekend.

    Holger

  7. #7
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    As always Andy beats the issue to the punch.
    Bravo, this is how things are done....proper way!!!

    Unfortunately most of the time wrong/unchecked and questionable info
    flows around and we all get caught in the mess, myself included.
    This post needs to be kept alive for future self-doers.

    Thanks Andy for the extra effort and sharing the info.

  8. #8
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    Thanks for the praise but I cannot take credit for the idea. I was just appling what I had found out on the F650 Chain Gang, thinking that our single spark engines would be even more suceptible:
    http://faq.f650.com/FAQs/PlugCapsnCoils.htm

    BTW, I added some clarification to my earlier posts to help explain the rationale better. I want to emphasize how hard I had to force my test leads to get my resitor and cap to measure 10kOhms before the mod. It is quite likely that had I measure the resistance including the plug prior to the mod I would have seen MOhms. Once apart, the spring and spark plug contact had some brass patina which I removed with a wire brush and some Scotch-brite. The resistor, even with the brass contacts sanded clean, never again measured in the kOhm range after disassembly, only 10-14MOhm. In the case of my brother's bike were everything was within spec, I doubt you would notice a significant improvement. If the resistor is like mine, showing signs of a gradual failure, I imagine the difference could be substantial. Oddly, my bike was running "fine" last time I rode it. Maybe I'll be in for a nice surprise in spring!
    Last edited by andysrage; 02-01-2013 at 06:28 PM.
    Andy
    2000 Pegaso Cube
    2016 CRF1000L Africa Twin

  9. #9
    apriliaforum expert
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    Spark Plug, Cable, Resistor Cap, ...

    Still you have laid down a good path for the self-doers.
    If you guys don’t mind I’ll throw some more sHtuff on the spark plugs-cables-caps, etc.
    Today almost all spark plug caps as well as spark plugs come with a resistor.
    The goal in the Pegaso case is to go with the lowest possible resistance number.
    The stock Beru cap came with only 1K Ohm resistance.

    In the case of NGK caps (called resistor caps) 5k Ohm resistance seems to be the lowest value.
    Andy, I think, once explained the need for the resistance, electrical interference, etc…

    As for the spark plugs…well they pretty much all have 5K Ohm resistance as well.
    The “thing” on the top of the spark plug where the cap sits on goes two, actually three ways.
    Where the thread is exposed, as on our DR8xx plug, it is called “terminal stud or thread or screw”.
    Where there is that shiny thing on the top, as on Brisk plugs, it’s called “terminal nut”.
    That type can be loose and solid. On the loose type the nut can simply be unscrewed, where the solid,
    as on the Brisk plugs, the nut is non-removable. Well…we know that even those can be removed,
    some people use file, grinder or “dremel” where others use some kind of lubricant and just unscrew the darn thing.
    The nut DOES NOT provide noticeable resistance.

    And in the case of our Pegasos…. the stock Beru cap as Andy showed us needs maintenance and eventually replacement.
    BTW that resistor cap should have only 1K Ohm of resistance.
    Here’s couple of links to learn more.

    NKG Resistor Caps

    Spark Plug Terminals

  10. #10
    apriliaforum Member koukosnest's Avatar
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    All i want from my birthday is another birthday!

  11. #11
    apriliaforum prov-nov
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    So folks,

    good informations here - i measured my ignition coil: zero ohm -> it was broken. Another spare-coil shows 9,18 kOhm, my red NGK-plug got 4,69 kOhm (~5 , as NGK says). The Beru resistor in the Beruplug got 1,16 KOhm.

    http://www.ngk.de/en/technology-in-d...al-resistance/

    U=R*I

    ~ 20000 V
    ------------------ = 1,442 A for the NGK-Plug
    13870 Ohm

    ~ 20000 V
    ------------------ = 1,789 A for the Beru-Plug
    11800 Ohm


    Does this make a noticeable difference?

    Holger

  12. #12
    apriliaforum Junkie SJL's Avatar
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    Cheers for another great "How to" fellas.

    Now does anyone have a part number for the resistor in case of eventual failure? I will be testing mine at some point this weekend.

    Cheers,

    Ste
    I am not an expert, please make your own judgement on diagnosis prior to doing anything drastic! I cannot accept any responsibilty for any work done on suggestions from me! If you are unsure, please contact your local garage.

  13. #13
    apriliaforum Junkie SJL's Avatar
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    OK, now here goes....

    I took my coil off today while removing the carbs for a cleaning, and the results so far;

    Mine is different to andysrage's coil, so here is a few pictures to see the differences.

    I tested prior to dismantling, and had a reading of 21k ohms. I then dismantled the plug cap and tested the resistor, which gave a reading of 5.9k ohms. I then cleaned the contacts on the resistor and on the other contacting parts in the cap and the screw in part, reassembled it and tested again which gave me a reading of 15k ohms for coil and cap (with same resistor in it). Amazing what a difference a bit of muck can do to electrics!

    The resistor on its own tested at 5k ohms after cleaning in case anyone is wondering.

    Click image for larger version. 

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    I am not an expert, please make your own judgement on diagnosis prior to doing anything drastic! I cannot accept any responsibilty for any work done on suggestions from me! If you are unsure, please contact your local garage.

  14. #14
    apriliaforum expert
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    Not to hijack the topic, but though to point on some really good prices at AF1

    Coil 0265355 $93 (less than BMW at $115)

    Chain Guide, U-Shaped 8120863 $5.99
    Exhaust Gasket (bushing) 8120823 $5.99

    You have to search for a specific item as they don't have all discounts listed under Specials..

    And ..on the topic....... here..... OEM Beru Plug Cap replacement for $13

    Going shopping!!!

  15. #15
    apriliaforum Junkie Unleaded's Avatar
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    I dont understand really all of this,i have old MK1 or GA Peg with rubber spark plug cap from NGK,is that good or not??

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