Resistor spark plugs?

[Pioneer]

Was just checking the spark of a torn down saw, and noticed quite a bit of difference in the spark quality between the champion fine electrode 5843 and cj7y.
The 5843 gave a pretty lame spark compared to the cj7y, and when I measured the resistance on both, I could get no reading on the 5843. Is it a resistor plug? One with an internal gap? Do we even need to bother with resistor plugs now that hardly anybody listens to the am band anymore?

 

[Efisher26]

I Think an “R” has to be in front of the model such as RJ17LM For resistor


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[MacAttack]

On any snowmobile, atv, dirtbike I've ever owned with a 2-stroke, i always tossed the resistor plugs and used non-resistor NGKs or Champions and they always seemed to go longer without a fouled plug. Never saw any downside to using non-resistor plugs.

 

[Andyshine77]

Some ignition systems need the resistor plugs to work properly. If the engine came with a resistor plug, that's what should be used.

 

[hotshot]

The 5843 gave a pretty lame spark compared to the cj7y, and when I measured the resistance on both, I could get no reading on the 5843. Is it a resistor plug? One with an internal gap?

I think the resistors were originally used to protect the CDI type ignition modules themselves on vehicles, and a side benefit was less radio interference...

I found one just like that (no ohm reading) a few weeks ago, but not the same plug number. It was a 5861, of the same type “cheaper” version they’re making now.

Throw it out!

 

[Yoopermike]

I listen to the A.M. Bands a lot as well as S.W. and HAM Bands as well.

 

[aokpops]

Can pretty much prove you will ruin a coil running a non resistor sparkplug . 2 or 4 cycle engines our will knock them out of time . Every manufacture I know comes with resistor plugs most chainsaws are bmr 7a I think . I switch a few years ago I was trashing coils in a matter of minutes . Like the engine would run 20 minutes an die . Or have a nice blue spark an not start or run because its out time .

 

[Pioneer]

Ok, after quite a bit of research, it boils down to this: On old points systems, use non resistor plugs. Resistor plugs require higher voltage which a points system may not be able to deliver in all running conditions.
If it has HEI, it will deliver the extra voltage required for resistor types.
Resistor types require higher voltage, but will have less amperage flowing through them. SOME coils are designed for resistor style plugs, and may be damaged by non resistor types by having that larger amperage flow. But how can you tell? For instance the Husqvarna 50 (HEI) is listed as having a non resistor type, and the Husqvarna 51 is listed as having the resistor type of the same plug. Are the coils different? Maybe, maybe not.
Use what it came with and you will probably have no problems. If you want to use non resistor types, make sure the ignition system has proven reliability with that type.