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What does this spark plug tell me?

Discussion in 'XJ Technical Chat' started by FrankEnsteiner, Mar 26, 2024.

  1. FrankEnsteiner

    FrankEnsteiner New Member

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    I posted a thread about a month ago. Long story short, new to motorcycles, bought an 82 XJ650 with 31k, PO said it couldnt start, price was right, now its mine. I have tried to work on it 4 days. Day 1, couldn't get it to start. Day 2, got it to start and rode it around the neighborhood for about 10 minutes. I convinced myself the guy just needed an excuse to sell it so he could get a new bike. Day 3, couldnt get it to start. Took the carbs off (which was a huge PITA), replaced the needles gaskets, emulsion tube, and the float needles. I noticed that one of the 4 long thin needles that go up through the brass color cylinder with a diaphram on top was not attached to the cylinder. Put everything back together, changed the air filter, and tried to start it. No luck. I also tried changing the fuel petcock. I pulled the plugs and they are coated in carbon. I did see some spark. I torched them to clear the carbon off, put them back in, but still, it just cranks and cranks. Any tips?
     

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  2. Brhatweed

    Brhatweed Active Member

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    Well the last of the fires were running fat (rich) so what I'm wondering here is have they carbon tracked enough to quench the spark or do you have another gremlin in the electrical that's keeping them from firing. You said "some spark" but is it strong and consistent? When it's cranking is there any sign of life like almost firing but not catching? If it's rich cranking but the plug isn't wet it should fire or at least fart if there's a strong spark. Have you checked the valves? Even just a few thousands off the seat it will leak down the compression while cranking.
    Battery up to snuff here and is there enough voltage at the coil positive while cranking to make a strong spark?
    How about the relays particularly the sidestand relay? Intermittent by chance? I'm looking at my 1981 SECA factory manual and the current path to the coils is thru the ignition switch via the brown wire then the 10 amp fuse and out on a red/white, those fuse holders are a sore spot so check them. The coil power is also a red/white and if all is well should be above 10V while cranking.
    Going back to the carbs these don't work well half-ass'd. The best advice I can give here is to click on the upper right hand corner where it says XJ4Ever and scroll down to IN THE CHURCH OF CLEAN and read up. This is about the best tutorial around and should be followed to the letter if you want your bike to run right. He knows his stuff and it's all from hard earned experience. There are numerous rebuild kits on the 'bay but none of them do any good without a good thorough & detailed internal cleaning of the carburetors. I found this out the hard way and now my 750XJ SECA cold fires literally right away with only 1/2 enrichment lever and no throttle. It idles like a sport bike with no puffing or speed droop and while I'm dealing with a lean issue due to an aftermarket exhaust it still pulls HARD enough to unload the front wheel in 2nd gear. These are snappy bikes but they need everything to be right to run right.
    Do you have a factory manual and if not need a copy of the wiring diagram? I can shoot you a high-res of the diagram and email it directly if you like as the server here won't let me upload something that big. Please let me know so I can take care of ya.

    We're praying for the victims of the bridge collapse out that way.
     
    Last edited: Mar 27, 2024
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  3. Melnic

    Melnic Active Member

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    Where in Baltimore are you ? I"m about halfway from Baltimore Beltway to DC Beltway.
    Don't have time this weekend to help but I may be able to help sometime later in person.


    I"ve gotten 2 XJ650's running in the past year and rebuilt 4 carb sets now for myself and others. I had 2 XJ650's 2 days ago but just sold one to someone. What Brhatweed said about cant half ass a rebuild.
    I'm hoping to do a video soon but the Mezmo engineering videos on the carb are great and pay attention to the path in the bowl that needs to be clear. Additionally, there is the pilot path that must be good for starting too.
    Those tiny holes get even partially clogged and it can affect idle mixture.
    Its a CV carb so it relies heavily on the fuel enrichment plunger to start. Cranking on the throttle won't do you any good on start up. you need IMO at least 3 of the 4 enrichment circuits to get it started and idling. Even so, w/o all 4 clear, it will be crap till fully warmed up and off the enrichment.
    As said, so many of the ebay/amazon kits are crap or have the wrong parts and such. Even if you don't replace the butterfly vacuum seals, a bike should run w/ just cleaning out the carb and replacing the needle and setting both dry and wet float levels (yes, do the wet level).

    Get new plugs! These should be zero ohm plugs if you have the stock resistive plug caps. Look up how to test a plug but a non resistive plug should be 0Ohm from tip to the end connector, not 5K and definitly not 100K (yes, I have pulled plugs on a recent bike and resistance was 400K!)
    Even if you have the bike mixture good, if you idle it a long time, the plug can turn black. We typically have our idle on the rich side I have learned and it starts/idles/accelerates from stop/runs better. On my bike if I let it idle for 10 mins and pull plug, its mostly black

    On plugs, NGK BP7ES is no longer made but there is some stock out there. Just don't use BP7RES , those are resistive.
    You can also use Denso W22EP-U
     
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  4. Brhatweed

    Brhatweed Active Member

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    I'm actually running resistive plugs on my 750 and not having any issues, they show just over 5K-ohms tip to end however I did ditch the resistive boots. All the resistor does is limit the overall current not the voltage until the arc is established and that in itself is basically a short at those voltages but if your ignition is compromised from age or wear the added resistance could make things difficult.

    One way I isolate carburetor & fuel issues is with the the use of a propane grill tank and regulator feeding the vapor into the air filter inlet. No wet fuel to foul the plugs and far less of a chance for burning thing from a backfire.
     
  5. Melnic

    Melnic Active Member

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    I ran resistive plugs with my resistive caps at the beginning and one cylinder stopped firing in less than 100 miles. Put in Non resistive and it started working. R plugs work for some people and not for others.
     
  6. Brhatweed

    Brhatweed Active Member

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    Guess they're Rated-R for mature users only?
     
  7. FrankEnsteiner

    FrankEnsteiner New Member

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    Hmm...so BPR7ES is what was in there, and I bought a 4 pack of the same on amazon. So those are resistive which is not what I want? Should have looked through the manual before I bought new ones! I will try the right spark plugs for one.

    Thank you for the offer Melnic. Do you post on youtube? I saw a video of someone in the MD area that had a vid on the XJ650's and it might have been you.
     
  8. Brhatweed

    Brhatweed Active Member

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    The R in the BPx7ES is resistor, the 7 heat range and I believe the E is extended reach, someone correct me if I'm wrong?
     
  9. Melnic

    Melnic Active Member

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    Yes, I have a few videos on youtube with the red XJ650 from my profile picture. I did the video before I put the cheap saddle bags on it.
     
  10. Dave in Ireland

    Dave in Ireland Well-Known Member

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  11. Brhatweed

    Brhatweed Active Member

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    Well here's what I found in my jugs after 200 miles. Definitely running lean.
    IMG_20240402_173656555_HDR.jpg
     

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