Spark Plug Wires

Outboards aren't supposed to use resistor plug wires are they?


(Specific engine I'm troubleshooting is '90 Johnson 200)

Re: Spark Plug Wires

Should be a solid core wire. We use ones with ss ends.

Re: Spark Plug Wires

That's what I thought. I've spent 3 days trying to figure out why my ignition was acting flaky when cranking the engine (trying to time it using the method in the top secret files). Finally I thought to check the plug wires and sure enough someone had used resistor wires.

Re: Spark Plug Wires

So that means they shouldn't use resistor type plugs then too, correct?

Re: Spark Plug Wires

mudvr1212 said:

So that means they shouldn't use resistor type plugs then too, correct?

Click to expand...

My understanding is that the resistor type wires do not withstand the vibration. Right or wrong I dont know.

Resistor plugs is another topic.

Suppressed plugs may be needed to suppress radio interference
The old method of suppressing interference was to incorporate a resistance in the plug.

These are fine with points ignition.

However OMC CD ignition systems do not work well with resistor plugs ( see http://members.iinet.net.au/~pauldawson/iame26-spark-plugs.PDF ) so if suppressed plugs are required to prevent RFI they must be inductive ( low resistance) types ... the Champion "Q" or NGK "Z" series.

I guess The CD ignition will not like resistor leads either!

VRO & OMS systems require suppressed plugs to be used and since motors with VRO or OMS will in fact have CD ignition it follows that "Q" (or "Z") plugs must be used.

Interesting to note that other brands of outboard motors do in fact use resistor plugs. Something quirky about the OMC CD system presumably!

Re: Spark Plug Wires

mudvr1212 said:

So that means they shouldn't use resistor type plugs then too, correct?

Click to expand...

I wouldn't say that. I checked some old plugs that were sitting on my desk at home last night, QL77JC4 as I recall (and they were OMC recommended plugs) and they show a resistance of 125 Ohms. Realize though, that's a big difference from the 900 Ohms that I measured on the plug wires someone had put in my engine.

Re: Spark Plug Wires

metriccrescentwrench said:

I wouldn't say that. I checked some old plugs that were sitting on my desk at home last night, QL77JC4 as I recall (and they were OMC recommended plugs) and they show a resistance of 125 Ohms. Realize though, that's a big difference from the 900 Ohms that I measured on the plug wires someone had put in my engine.

Click to expand...

QL77JC4 are low resistance, inductively suppressed plugs .. The type used with OMC CDI systems.

Ordinary resistor plugs have a resistance around 5 kΩ.

Re: Spark Plug Wires

I have a 73 johnson 25 horse. I can't recall the plug in it now. Just to see if it's the correct one, what plug does the man. recommend?

I'm almost positive there is a Q on the plug.

Re: Spark Plug Wires

mudvr1212 said:

I have a 73 johnson 25 horse. I can't recall the plug in it now. Just to see if it's the correct one, what plug does the man. recommend?

I'm almost positive there is a Q on the plug.

Click to expand...

J4C is the currently recommended plug, gapped at 0.030"

Re: Spark Plug Wires

Thank you!