Spark Plug Wires... What To Do?

[J6G1Z]

Has anyone found a set of replacement spark plug wires for the VT Ascot?

Is there a suitable automotive plug wire that can be adapted? How about the ends?

Should I be looking for resistor or non-resistor wires?


Thanks
J.

[Buddy]

For wire I've used metal core non-resister wire. You should be able to find it in bulk at a lawnmower shop or a well stocked auto parts store. I have even bought a set of universal metal core wires made for an old tractor and cut them down to fit.

The ends are a different story. If you use non-resister wire you'll need resister caps. The NGK caps I've used come in different resistance. The angled caps for the outside plugs are part number XD05F. Which means they're 5 ohm. I'm still running stock straight caps.

I've heard of people running automotive resister wire with plain ends, but I have no experience with that.

Hope that helps,
Buddy

[J6G1Z]

What is the resistor for? Just radio interference?

If that is all, would it be better to have non resistor wires, boots & plugs?


Thanks
J.

[Buddy]

From what I understand, the igniters, coils, wires, caps, and plugs need to have the right combination of resistance.  Come to think of it, you might could run resister plugs with resister wires and plain caps and be ok. I don't know what the VT coils are rated at. You might see what Dyna or Accel list as stock replacement. Dyna coils are color coded. I used brown 1.5 ohm ones on a  BMW airhead, and green 3 ohm ones on my old Suzukis. I think black is 5 ohm. There may also be blue ones.

Buddy 

[J6G1Z]

Well, I spent a couple hours replacing the spark plug wires yesterday. I bought 5' of 8mm solid core wire from NAPA. NAPA has both 7mm & 8mm solid core wire. I went ahead & bought the twice as expensive 8mm wire. It's nice wire & easy to work with, unfortunately it is colored light blue vs. black. The hardest part was just removing the rubber bushings & ends from the old wires to transfer over to the new wires. The new wire was just thick enough to barely fit inside some of the boots, etc, but a light coating of dielectric grease allowed everything to slide into place. The ends threaded right back on. I did one wire at a time & made the new wire about an inch or so longer. That was a mistake. Now there is excess wire tucked away. I covered several sections of wire with some heat shrink tubing to provide abrasion resistance. Other than the wires being blue & sticking out a bit when you look at the bike, the project was a success. The bike fired right off. Can't really tell if it runs any better, but it does have brand new wires now... Well except for the plug boots.

A good afternoon project for anyone who wants to insure that the spark energy is traveling down a fresh wire.

J.

[J6G1Z]

Here is an informative reply that I received on the Yahoo VT Ascot Owners Group


The original purpose of resistance in the secondary circuit was to reduce radio interference. But there are other advantages.

1. “Radio” interference doesn’t only mean “car radio” interference. It really means “radio-frequency” interference, or, even better, “electro-magnetic” interference. This includes cell phones, GPS navigators, engine-control and ABS computers (which we don’t have, of course), pacemakers, etc. In other words, anything electronic that’s close by. The less the interference, the better these things work.

2. By putting some of the resistance in the secondary wiring, there is less power dissipated in the coils. That’s a good thing. On the Ascot, the coil secondary is about 25K ohms. The plug caps are about 5K ohms and the plug itself is about 1K ohms. So the total secondary circuit is 37K ohms. The power dissipated in the coil due to the secondary current is reduced by about 12/37, around 30%. With our coils, every little bit helps.

There’s really no performance penalty to including resistance in the circuit. Before the high voltage jumps across the plug gap, there’s no current flow, therefore no voltage drop across the resistance. So the full voltage appears across the plug gap. Once the plug fires, you don’t need a lot of voltage (because the gas in the cylinder is ionized and therefore conductive), so you don’t care about any voltage drop across the resistance.

The downsides are cost and reliability. But the vast majority of ignitions now use resistance in the secondary circuits, so the cost penalties have been minimized (in fact, it’s hard these days to even find non-resistor plugs). The reliability issue relates to the carbon-core wires used in cars, which won’t stand up to the vibration in motorcycles—that’s why most bikes use solid-core wires with separate resistors built into the plug caps.

HTH,
Neil