XJ650 - Misfire with colortune/non-resistive plug

Got a weird one to report, and I’m kind of stumped about the cause. My bike came to me with resistive spark plugs, but seemingly OEM coils and plug caps. I changed them out for non-resistive spark plugs per my owners’ manual, but recently I noticed a misfire on cylinder #2 when idle.

I did a bunch of carburetor work on carb #2 during the off-season, so I immediately suspected the carbs. However, I had just recently (about a week ago) synched the carbs, and I wet set the fuel level when I finished my work on carb #2.

I got out my colortune spark plug so that I could set the mixture, but when I put it in, I got electrical arcing on the outside of the colortune. Tried it on all the other cylinders, no arcing. So, I put electrical tape around the core of the colortune, which solved the arc. But still, it was misfiring and making it incredibly hard to adjust the idle mixture screw.

Eventually, I reinstalled the (old) resistive spark plug, and the problem seemed to resolve itself. All of the other cylinders have no issues with the non-resistive plug, but not cylinder #2. Has anyone ever experienced something like this? I suspect the #2 plug cap may be a non-resistive type, but shouldn’t the colortune still work in that case? Is my coil suspect?

Any help would be appreciated.

 

Sorry for the double post. Just realized I can upload some videos to YouTube. Here’s it misfiring with the colortune:

https://youtube.com/shorts/6namy8UGqHo?si=LIzONdK0p2_XvehA

Here’s it smoothed out with a resistive plug:

https://youtube.com/shorts/U37GQMFxSV0?si=UldRbm-pdKFWZy3e

 

Hah, you should see the arcing in a XJ700X with the deep plug wells. I have not found a way around it yet.

 

I assume you are using the screw-in "extension wire".......if so, install the wire onto the plug before installing plug and wrap the connection with electrical tape. Then install combined unit.......yes, it's a pain in the butt to do it this way, but in reality, all you have to do is get the Colortune hand-tightened/snug into the spark plug hole, it doesn't (and shouldn't) be torqued down as if it were a real spark plug. That should cure the arcing.

 

How does electrical tape prevent arcing out the sides of the wire? I did run the wire into some silicone tubing but that didn't help.

 

Electric arcs happen when the voltage difference between two conductors is high enough that the electrical resistance of the air is no longer enough to prevent current from flowing. If you can add more insulators between the high voltage (plug and wire) and low voltage (cylinder head) parts, you can mitigate arcs. Though, it’s kind of crazy that silicone tubing wasn’t enough to help. Must be an extremely narrow plug well. Electrical tape was enough for me, even though I was getting arcing between the wire and the outer portion of the colortune itself.

 

Is it arcing out of the black "insulated" side of the wire? If so, the insulation is cracked, and you might need to wrap the entire "extension" piece tightly with electrical tape.

 

I have tried the wires from two new colortune kits, same results. They don't like plug wells. Even with the plastic cylinder with the mirror used, I get arcing.