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86 XJ700 coil to cylinder total resistance.

Discussion in 'XJ Technical Chat' started by Huntchuks, Dec 4, 2019.

  1. Huntchuks

    Huntchuks New Member

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    My son gave me an XJ700 Maxim that he bought but didn't use. The thing doesn't like to start except with much cranking and starting fluid in the airbox. If it started it would fly. So far I changed the rectifier (wasn't charging), pulled and cleaned the carbs and checked the ignition coils. The coils had correct resistance at the primaries and secondaries. The next issue is the plug caps. The outside caps have 10k resistance but the inner two only have 5k resistors in them. My understanding is that they should all be 10k. The existing plugs are non-resisters although one seems to be bad at 3k. Doing more research, I find some conflicting info. In this post by Chacal (forums/threads/plug-caps.33166/) is this:

    It is important to remember that you should strive to keep the ignition coil secondary circuit (plug wire, plug cap, and spark plug) total resistance as close as possible to original specifications, which are:

    - 15K ohms per cylinder on all 1986 XJ700-X, XJ750-X, and XJ900 S/SH models.
    - 10K ohms per cylinder on all XJ550, 1985 XJ700-X models, 1986 XJ700 non-X, XJ750RL, and XJ900 N/FN and F models.
    - 5K ohms per cylinder on all XJ650, 1985 XJ700 non-X, all 1981-83 XJ750 models, XJ750-D, XJ900RK and RL models, and XJ1100 models.

    In his catalog (catalog/d-6-ignition.html) there is some conflict, may just be typo:

    XJ700 air-cooled models:

    Pick-up coils:
    120 ohms +/- 20% = 96 ohms to 144 ohms acceptable range

    Ignition Coils:

    Primary side (input from main wiring harness):
    2.7 ohms +/- 10% = 2.43 ohms - 2.97 ohms acceptable range

    Secondary side (spark plug wires, without their end caps):
    12K ohms +/- 20% = 9,600 ohms - 14,400 ohms acceptable range


    Spark plug caps:
    1985 N/NC models: 5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
    1986 S/SC models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range


    Spark plugs:
    1985 N/NC models: 0 ohms per plug
    1986 S/SC models: 5K ohms per plug

    In this case the total resistance would be 15k per cylinder. Is this just a typo?

    Later in his catalog:

    XJ700 engines:

    HCP1294 Original BP8ES NGK SPARK PLUG, stock non-resistive plug is correct for all 1985 XJ700 non-X models. Each:
    $ 4.95

    HCP1294SET4 Original BP8ES NGK SPARK PLUGS, set of 4.
    $ 18.95


    HCP1295 Original BPR8ES NGK SPARK PLUG, stock 5K ohms resistive plug is correct for all 1986 XJ700 non-X models. Each:
    $ 4.95


    HCP1295SET4 Original BPR8ES NGK SPARK PLUGS, set of 4.
    $ 18.95

    I am also assuming the bike is an '86 model by the VIN (and registration).

     
    Last edited: Dec 4, 2019
  2. Huntchuks

    Huntchuks New Member

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    Also should note that the 5k caps are TD T-133, which I assume should be 5k. Are they correct for this bike?

    The Chacal catalog says:
    T-133: used on all air-cooled XJ650, XJ700, 1981-83 XJ750, XJ750-D, XJ750RL, XJ900 RK, RL, N/FN, and F models, and XJ1100 models on the inner cylinders (#2 and #3).

    That would indicate I have the right caps and they have 5k resisters. If so, why are the outer caps at 10k and all plugs non resister?
     
    Last edited: Dec 4, 2019
  3. Polock

    Polock Well-Known Member

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    are you trying to make it original or just make it run good?
     
  4. Huntchuks

    Huntchuks New Member

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    Make run first and then make it run good.
     
  5. jayrodoh

    jayrodoh YimYam Premium Member

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    This sounds carb related and not electrical. When you cleaned the carbs did you clean out the enrichment well? This is a very common area to plug on these and requires special attention, the usual spray/soak in the cleaner will not do it.

    Probably due to a previous owner.

    Does the bike run after all the cranking and spraying with starter fluid? If so, your issues are probably not related to the plugs and caps although you should replace with the proper ones when possible.
     
  6. Huntchuks

    Huntchuks New Member

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    Thanks. The carb enrichment plungers areas were disassembled and cleaned. Truth be told, the carbs were very clean internally but I cleaned everything anyway. Right now I can't get it started (cold weather doesn't help) so I started looking to ignition problems. I would like to make sure I have correct plugs and caps but I still don't know what is correct. Many places show the plugs as NGK BP8ES (2912) which are non resistor plugs. That is what is on the bike but the two outside caps are 10k and the inner are 5k. I am confused.
     
  7. jayrodoh

    jayrodoh YimYam Premium Member

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    The enrichment plungers are fed by a tiny tiny jet in the bowl, they plug very easily. I've circled them in red below, you should be able to shoot carb cleaner clear across the room when spraying in the upper hole (watch your eyes). If that is plugged, bike will be very hard/impossible to start. It should start even in 20 degree weather.

    well.jpg

    Might be mix of parts from different years, here are the specs for the 700:

    Spark plug caps:
    1985 N/NC models: 5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
    1986 S/SC models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range
     
  8. Huntchuks

    Huntchuks New Member

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    I didn't do the squirt test. I'll pull the bowls and check it out.

    I have seen that spec many times but the confusion comes from this bunch of info (see original post):

    - 10K ohms (total) per cylinder on all XJ550, 1985 XJ700-X models, 1986 XJ700 non-X, XJ750RL, and XJ900 N/FN and F models.
    Spark plug caps:
    1986 S/SC models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range
    Spark plugs:
    1986 S/SC models: 5K ohms per plug
    HCP1295 Original BPR8ES NGK SPARK PLUG, stock 5K ohms resistive plug is correct for all 1986 XJ700 non-X models.

    As you can see, 10k caps plus 5k plugs = 15k but there is only supposed to be 10k total per cylinder. Other places say the NGK BP8S is the stock plug.

    T-133: used on all air-cooled XJ650, XJ700, 1981-83 XJ750, XJ750-D, XJ750RL, XJ900 RK, RL, N/FN, and F models, and XJ1100 models on the inner cylinders (#2 and #3).
    The T-133 caps are supposed to be stock and they are on my bike but they only have 5k resistors in them.
    I am still confused. Should I be using NGK BP8S (zero resistance) plugs in the outside cylinders that have 10k caps and BPR8ES (5k) plugs in the inner cylinders that have the 5k caps?
     
  9. jayrodoh

    jayrodoh YimYam Premium Member

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    Ah I can see your confusion there. I don’t have a 700 nor a service manual so I am not sure. Maybe another member might clear this up or @chacal can clarify. Did you try emailing him?
     
  10. Polock

    Polock Well-Known Member

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    i don't want to dismiss your plug cap question, but your coils are 30+ years old. it might be wise to just replace them with honda 750 coils, wires and caps. then that part of the bike is done.
    @Jetfixer has this down. personally i use dyna coils, copper wires and caps and iridium plugs
    clean out those enrichment jets, a steel guitar string is the prefect tool, damm if i remember the size though
     
  11. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    1985 air-cooled XJ700 models used the "traditional" non-resistive spark plugs (zero ohms) and 5K resistive plug caps, thus 5K ohms per cylinder total secondary circuit resistance.
    1986 air-cooled XJ70 models used 5K resistive spark plugs along with the same 5K resistive plug caps, thus 10K ohms per cylinder total secondary circuit resistance.

    The water-cooled XJ700's followed the same pattern: the spark plugs went from non-resistive on the 1985 models to 5K resistive plugs on the 1986 models. Of course all of the X models used 10K resistive caps, so the 1985 models had a total of 10K per cylinder (using the stock non-resistive plugs) while the 1986 models has 15K resistance per cylinder (10K caps and 5K resistive plugs).

    Although I can't say for sure, I seem to recall that this sort of change occurred on a lot of models at about this time...…...going from non-resistive plugs to resistive plugs, probably due to an emissions and/or an electrical-interference issue.

    I don't know why the current Yamaha parts diagrams shows using 5K center cylinder caps and 10K outer cylinder caps.....that's not the way that they were originally specified or equipped.
     
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  12. Huntchuks

    Huntchuks New Member

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    Thanks for the info. So, if I want to keep my coils for awhile I need non resistor plugs in cyl. 1 & 4 with the 10k caps and resistor plugs in the cyl. 2 & 3 with the 5k caps?
    I lost the little disk (what is it, about .005" thick?) when I pulled out one of the 5k cap resistors. Is this necessary to replace or can the resistor make direct contact with the spring?
     
  13. tabaka45

    tabaka45 Well-Known Member

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    Did you replace the brushes in the alternator? That solved my starting problem. I was having a starting problem similar to yours, and sometimes it would finally start and then shut down, especially if I hit the breaks. When I mentioned the breaks someone suggested that I check my voltage at idle, which turned out to be about 11.2 volts, when it should be well above 12 volts. ( I was only getting abut 13 volts at 3000 RPM) Apparently, 11.2 volts is not enough for good starts and just adding the additional drain from break light was enough to shut it down.
     
  14. Huntchuks

    Huntchuks New Member

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    I haven't checked the brushes yet but that will be coming now that you reminded me. I did replace the rectifier and it charges at RPM's but not sure if enough at idle. Another thing to check but need it running first.
     
    Last edited: Dec 5, 2019
  15. Huntchuks

    Huntchuks New Member

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    Anybody know how cold is too cold to check and replace valve shims? 25F - 40F nowadays but have no heated space to work.
     
  16. Huntchuks

    Huntchuks New Member

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    Checked the brushes and they are long, 9.2 mm to the wear lines. How long are new ones?
     
  17. jayrodoh

    jayrodoh YimYam Premium Member

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    25 to 40 is fine, I don’t think there is a too cold, if it’s too cold for you to work then it’s too cold :D:D
     
  18. jayrodoh

    jayrodoh YimYam Premium Member

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    If they are not to the wear lines you don’t need to replace.
     
  19. Huntchuks

    Huntchuks New Member

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    Thanks, I was wondering how the cold would affect the measurements. Resistances may be off on this cold also.
     

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