82 GS850GL strange no spark ,spark on cyl 4?

[jon]

So I have a a problem I have never seen before and dont know what to make of it. From time to time my bike starts running on 3 cylinders, which leads to me takeing apart the carbs ,checking the coils,ect. And by chance, changing the plugs which fixes the bike unbeknownst to me. Until it happens again. Today I accidentally discovered something while checking the spark. Cyl. 4 (I believe, all the way to the right.) Does not spark while the plug is in the plug wire, and touching the head(the other 3 do) but when I pull itaway it starts to spark as well as jump from the head to the plug. So it sparks when not grounded . And it does this on all for cylinders. And if I grab another plug ,it sparks as it should ...when grounded to the head on all for cylinders. Furthermore I found the last set of 4 plugs I had in last year and it was the same way. One plug out of 4 would only spark once it was removed from the head or surface I was useing to ground it while cranking the engine over. Any thoughts as to what could cause a plug to start acting this way or how it is even possible?

[Redman]

. .
when I pull itaway it starts to spark as well as jump from the head to the plug. So it sparks when not grounded . . . .

Tried any substitution? Such as move the suspect #4 plug to another wire and see where/if the suspect symptom moves to??

Also: Do you know that the plug caps (if stock type) have a resistor in them, 5K ohm, that can go bad (open). And the caps can twist off the wire. So can substitute them around too.

[pdqford]

I suspect the spark plug is bleeding the high voltage into the base of the plug and into the head without having to jump the spark plug gap.

When you take the plug base away from the cylinder head, the high voltage jumps the gap between the plug base and the head. This causes the voltage to surge through the spark plug and arc across the spark plug gap. This voltage is so sudden it doesn’t have time to leak around the spark plug gap.

Make sure that plug’s gap is not excessive, that there are no carbon tracks or hairline cracks in the plugs porcelain, and that the porcelain is sealed to the plug base.

[jon]

It may be had to follow but in what I wrote it says I did all that. And the ignition system is ll brand new ngk and green coils.

[jon]

What your saying makes sense but it has happened to 2 sets of 4 plugs in a row and maybe more. Its seems like something must be causing the plug to malfunction. I'll check the gap tomorrow. Do you happen to know what the gap should be?

[cowboyup3371]

It’s in your service manual. If you haven’t got one yet, go to http://members.dslextreme.com/users/bikecliff/ and download it