Why replace spark plug wire?

[QBS]

Over the years I have seen many recommendations to replace the spark plug wires on Vs and other old bikes.  I'm pretty sure that what was being recommended was replacing the wires and their caps.  If so, why both the the wires and the caps?  Why not just the caps?  Copper doesn't wear out,..... but the caps do develope corrosion and mechanical failures, so why not just replace the caps and retain the wires.  Or, as suggested in another recent posting by JasonM, repair the cap and save even more money.  V wires are very heavily insulated and well protected from rubbing wear for their entire length, so the chances of a voltage leak developing seem to be remote. 

The entire proposition stated above is strictly addressing copper wires.  Carbon core wires are not included.

[Tiger]

 :) This is my take on this subject...

When I was a kid, my dad would always, on a "new" used vehicle...cars, bikes...change the plugs, wires & caps (along with points, condenser, etc) to eliminate the chance of bad starting, brake downs, what have you... Long term cheap insurance was how he put it... ;)

When I began my automotive apprenticeship back in '69, the mechanic that I was serving under had the same principle... ???

Consider that, in most cases, we acquire these rides cheap and in varied states of decay...with twentyfive year old weathered oem wires (and sometimes caps). We then go ahead and spend money on paint jobs, a good set of tires, a new battery, handlebar grips, polish, led lights, whatever.......and leave out an integral part of the ignition system!!! 

They have paid for themselves over 25 years of extreme heat, cold, the elements, etc, etc.

I don't see repairing such inexpensive part's/clipping back wires, as a viable alternative...unless your at the side of the road!!!

Spending an extra $20.00 on my Vision's is cheap insurance, indeed... 8)

                          8).......TIGER....... 8)

[inanecathode]

As i see it, nothing really happens to the wire itself, or the carbon if you use that. Maybe the ends can corrode but nothing is really wrong with the conductor when a wire change becomes necessary. The insulator is what goes bad, it cracks or develops pin holes that leak voltage when they get wet, when the spark plugs are loaded heavily, or the wire moves close enough to another conductor.

[George R. Young]

Simple enough test, take a running bike, put the garden hose on fine spray, and direct at plug wires. Any misfiring indicates something needs replacement.

Had to replace the RD350 plug caps on a trip, any time there was rain or fog it would start misfiring (and then foul the damn plugs). Never had any such problems with the Vision.

[Lucky]

something else QBS, your bike, i think, is atypical of many Vision owners bikes.  often they were left outdoors or neglected/abandoned for years in all sorts of hostile conditions, (heat, cold, salt air, etc). i know your bike hasn't been subjected to those conditions, so you might have forgotton what a toll they could take on the rubber.  i suspect that's the reason for most replacements.

my .02
--Lucky
(still here)

[Brian Moffet]

I don't the info behind QBS's bike, but I know mine didn't need to worry about the sparkplug wires.  I replaced them when I did the rebuild because they were 25 years old.  Not because the needed it.

But, I know the entire history of my bike.

Brian

[arthurdent510]

For cars it's recommended that you replace them every few years, but people rarely do.  I race my Miata and have seen multiple dyno graphs for old spark plug wires vs new ones.  The copper doesn't wear out, but it does build up resistance which makes it harder to push current through.  While it may be small, I've seen up to a full horse power gain just by changing out wires.  There are claims that it also increases throttle response, but that's subjective and can be taken however you want  :P

[Kenny]

  Cutting a 1/4 " off the resistor end of the plug wire takes care of the corrosion. Remember most of these bikes have 100,000 or less miles,and sure the elements u/v , moisture of course take a toll on the components.
              Tune em up.. Ride Safe. Ken S. ;)

[Rick G]

Electricity travels on the surface of  a wire (that's why some are multistrand)
If the wire has oxidation or corrosion it will inhibit  the current from flowing.

When working on old bikes, I just cut the last 3/8 of an inch off. On my bike it got new wires . I was able to find copper core spark plug wires  at a small engine shop. I wouldn't use carbon core wires on any bike!