Plug cap arching - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 6 (permalink) Old 08-13-2016, 01:08 PM Thread Starter
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Plug cap arching

About 2 weeks ago I took a ride in the am before it got real hot out. On my way home,turning on to my road ,bike started missing,then shut off. I was still rolling,then the dash lights came back on so I let the clutch out to pop start it. Pop it did with a huge backfire,but I pulled in at home and shut it off. After it cooled I took the seat off to check the battery connections,sure enough,loose ground wire. I cleaned all battery connections. Bike fired up no problem. Here's my trouble. Next morning early,still dark I started my bike and in the dark I noticed the right rear spark plug cap arching out against the cooling fins. Last spring I noticed the same thing happenning so I bought a new NGK cap and wire and replaced it. The old cap had no cracks that I could see but changed it anyway. Now I notice the new one doing the same thing, I inspected it,gave the cap a little turn on the wire and even taped over the wire,boot and cap. Bike runs great,can feel no skips or misses,even had my brother in law listen as I left his house hard,letting up to 6k rpms in 2,3,4,he said sounded good and I was flying. It still arcs a little,but seems to stop after it warms up??Thought maybe the humidity???Should I just leave it and ride it.I don't want it to lead to some bigger problem.Thanks.
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post #2 of 6 (permalink) Old 08-14-2016, 03:02 AM
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What a weird problem. I'm surprised that it would arc that far even if there was a big 'ol crack in the insulation.

Anyway, if it is arcing there, it probably isn't arcing at that plug ... path of least resistance and all. Have you pulled that spark plug to see if the electrode is still good, has proper gap & is sparking? Might be hard to do an accurate test since removing the spark plug will moving the spark plug cap too far away from the engine block to arc, so you might get spark on the plug while testing out-of-cylinder even if it isn't sparking in-cylinder.


Since each cylinder has two spark plugs, one plug might be dead but the other plug keeps the other cylinder firing.

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post #3 of 6 (permalink) Old 08-14-2016, 09:54 PM Thread Starter
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Thorn,the Iridium plugs were changed the same time I changed the arcing cap and wire,and only have a few thousand miles on them. But just to make sure I will check each plug for gap,spark starting with that one. It's easy enough to do,so why not. I thought maybe the humidity,my bike was sitting in a puddle after some storms blew through,and with 100% humidity,the water didn't even evaporate. Steam was coming off my bike as it warmed up,unbelievable,thanks.
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post #4 of 6 (permalink) Old 08-15-2016, 05:08 PM
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Try dielectric grease to see if that helps.

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post #5 of 6 (permalink) Old 08-15-2016, 06:19 PM
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Check the gap on your plugs. You could find some rubber and insulate the wire and caps better. The plug wire on the right side of the bike has been known to spark against the fin, never heard of the cap doing this.
Make sure you don't have resistor caps.

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post #6 of 6 (permalink) Old 08-17-2016, 12:14 AM Thread Starter
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I pulled the plugs starting with the right rear,and I read in the plug thread where you should not hold the ceramic with your bare hand as the oil from your hand might cause problems. I honestly cant remember if I touched the ceramic when I first installed them. Anyway,the plugs looked nice light tan,no hot white,and not wet either. I held the plug next to the fin on the head and it was sparking,I didnt get shocked either as I was holding it by the cap.Checked the gap,Iridium plugs .034in. Put on never seize back on and put them back in.The cap looked good, NGK long XDo5F.Took it for a morning ride,didn't see any arcing,but this time before starting I gave it a little spray of WD40 on the cap and wire. Maybe it was just the crazy humidity lately ,as the bike ran good. As far as dielectric grease,would I rub that on the wire,cap,???As for now I guess I'll just run it. Thanks.
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