Resistor Spark Plugs - Needed or not ?

[Born2Mow]

When I started working on engines in the mid-60's, there were no resistor wires, caps, or plugs. It was quite common to hear the sound of the car's ignition on low-end radios. Seems the spark gap is little more than a cheap RF generator. Then about 1969, cars started using resistor plug wires for suppression to eliminate this noise.

I am aware that systems designed NOT to have resistor ignitions will suffer when any of these resistor elements (plug, caps, wires) are added, and it's something to watch for when tuning classic vehicles. But what happens when the resistive elements are removed from modern ignition systems that were designed to have them ? Obviously, we're back to generating RF noise, but what happens to the quality of the ignition spark ?

 

[Scrubcadet10]

I don't know of any lawnmowers with AM/FM radios

 

[Hammermechanicman]

Resistor plugs came out in 69 but carbon core wires had been around since the late 50s. Some tractors with 6 volts systems don't like resistor plugs or wires if the battery is weak. It will crank the engine but the low voltage to the coil can't overcome the resistance/gap. Most old tractors with magneto ignitions can have the secondary coil in the mag ruined from using resistor plugs and wires. Other than RF noise or possibly messing with electronics removing the resistance from the plugs and wires won't hurt an ignition system. I have seen some cheap hand held 2 strokes run poorly when switched from a regular plug to a resistor plug.

Back in the day when i towed heavy with my 1990 pickup i installed a high energy multiple spark discharge MSD ignition in my truck. Instructions said to only use spiral wound solid core wires. Well holy crap! I bought very high quality wires and every 5000 miles or so engine started running rough and missing bad at idle. Had to change wires and plugs to fix it. I bought some of the best wires summit sold and it would still burn them up. I had to change plugs and wires almost as often as oil. It could jump an arc almost 2 inches. At low speed it provided multiple spark discharge. At higher RPM just one massive spark. I still have it if somebody wants it. Has a timing retard control that is adjustable from drivers seat. You CAN have too much energy in an ignition system.
Back in the go cart racing days pit myths were everywhere and one was that a resistor plug fired slower and had retarded timing vs a non resistor plug. Numerous times we checked it with a timing light. We never found a difference up to 6500 RPM. If we opened the gap up to the point it starts to miss we got about 1/2 to 1 degree of difference. We used offset keys to adjust the timing. You kept moving up the timing up till the cylinder head temp started going up then backed off a couple degrees.

 

[Hammermechanicman]

I don't know of any lawnmowers with AM/FM radios

I once saw a JD front mount commercial mower with an AM/FM radio and an RV roof A/C unit. I was totally impressed.

 

[bertsmobile1]

Some magnetos are matched to a particular resistance.
I can remember LC Yamahas always ran bad unless you had the right plugs and they were also gapped within the specs.
Right now there is Kohler confidant in the workshop.
It had a random miss .
Not having the spec XC12YC plugs I popped in a pair of NGK "equivalents" and the problem was still there so the carb got stripped and I spent a week faffing around till the right Champions turned up .
Put the right plugs in just in case and it did 20 perfect hours being tested in 4' high grass and never missed a beat , so it looks like for some engines it does make a big difference.
As an aside these plugs were only 60 hours old but were snowy white ( too lean for my book ) but there were no leaks & the carb was as clean as one would expect for those hours.

 

[StarTech]

RF noise is still a problem. It affects the newer electronic ignition system and computer controls. When alternators first showing in vehicles They produced RF noise too and still do. I remember having to install RF filters on both the power supply leads and the antenna leads.

BTW I can still really mess up touch control lighting when my CW transmitter arcs the antenna tuning capacitor plates..