4th Spark Plug resistance issue

[jbethune]

Hi,

My '84 nighthawk 550 was not firing on the 4th cylinder until I hit about 5000rpms, and then it would kick in. You could easily tell when it kicked in and its was around 5kprms every time. After significant riding, you could tell it wasn't always firing because the exhaust was relatively cold out.
So, I replaced the lead to the 4th spark plug, and put a new 5k NGK cap on it. For the first day or two it was driving fine, at full power. However after about two days, the bike has regressed to the state I mentioned above.
Does anyone have any ideas what might be causing this?
Thanks
Jeff

[Johnj]

Have you tried moving the spark plugs around (1st to 2nd, 2nd to 3rd, 3rd to 4th,and 4th to 1st) to see if the problem follows the plug?

[jbethune]

I have moved plugs and replaced plugs, but that was before I replaced the whole wire and plug cap. Moving the plugs didnt make a difference.

Thanks

[BRUMBEAR]

try moving coils and wires? I think you have a coil or a wire breaking down.

[jbethune]

Yeah, since I replaced the wire causing the initial problem, I guess i need to replace the coil that produces the charge in that wire?