Spark Plug Caps

[kkrazyt85]

I need to know which caps to purchase...I found these on Dennis Kirk.com
20788 - Spark Plug Cap
Manufacturer - NGK
Type - Plug Cap
Size - 14mm

They are 90 degree waterproof....any help is appreciated since I just gor this bike and am restoring it....

[skids]

Get longer ones for the inside plugs if you buy the 90 degree bend. I can't help you with the diameter spec. sorry.

[strom]

AFAIK you need two 120 degree and two 90 degrees, 5kOhm resistance.

LP

[TopCatGr58]

"X"cuse my ignorance here,

I remember someone posting a nice picture showing the guts of a plug cap, which included the little ceramic resistor inside, about 5K ohm! If we have/use resistor plugs, then why is a resistor needed inside the plug cap?? Does the coil need some/a little resistance/more than the spark plug alone to make it work without drawing too much amperage thru the secondary circuit when it fires!? Is the resistor merely for RF noise suppression? Could we not just remove the resistor, replace with a piece of metal/conductor so that the plugs would be getting ALL of the current being sent to them!? I'm not an electrical guru, just have a basic understanding of DC circuits for trouble shooting, so hopefully someone can enlighten me/US!

[TopCatGr58]

Well, after posting my query, I then redid my search and looked at ALL of the threads, 25+, and came across this reply from Gary Granger:

Here is my theory, not supported by any known facts: I believe they will work. Regular car wires are resistive, but the caps are not. On bikes usually the wires are non-resistive and the caps are resistive. The whole deal with the resistance of plugs, wires and caps is confusing. I was told that they started making resistor plugs to eliminate radio interference. This makes sense, but most motorcycles do not have a radio. They do however have electronic ignitions and other electrical devices that may be affected by spark pulses. So I think one of the 3 things should be resistive (plugs, wires or caps) but not all 3. Racing engines use non-resistive wire, plugs and caps to allow maximum spark energy to hit the mixture. In reality though I have used resistor and non-resistor plugs interchangeably, with no difference in performance. I think the reason cars use the resistive wire cores is for flexibility, cost and manufacturing ease not for radio interference.

I think there is a tech tip showing regular plug wires on the old coils.

Read this it answers most of the questions about plug wires and how/why they are made the way they are.
Truth about ignition wires

This whole site has some good info on plug wires and effects of RF and EM interference in plug wires.

Magnecor Race Wires

__________________
Gary Granger
Remember, we are the caretakers of mechanical art.

T.C.

[TopCatGr58]

Okay, so after reading those articles, it says we need to use RF/EMI suppression wires "IF" we have a lot of those fancy computer controlled devices like emissions controllers and such!? We only have a TCI!!!

Hey Randy, is our TCI unit susceptible to these forms of RF/EMI produced from the wires/plug caps/plugs if we don't use suppressor wire/caps/plugs!?

I've been thinking about getting some new plug caps, and was wondering about removing those little ceramic resistors to allow more juice to get to the plugs!? Good/bad/indifferent idea!?
I'll stop answering my own replies now! T.C.

[freebird01752]

kkrazyt85,

I just picked up a set last week at my local dealer. It took a couple of days to get them. These are the resistor plug caps.

NGK # DSLD05FP out side plugs 2.35 each
NGK# DSXD05F inside plugs 3.30 each


Steve

[crunchbird]

My #1 and #4 caps failed--the wires had arced/burned, caps fell off. I soldered on some heavy wire and for some time ran it wrapped to non-resister plugs. No problem for me. People around me listening to AM radio may have been unhappy, but aren't they always?

Once in a while I'd get zapped resting my leg up on the crash bar, now I have some cool MSD caps.

"Don't drive, it makes you stupid."

[randy]

T.C. ;

A resounding NO!

Our TCI boxes will not be effected by the type of RF interference generated by spark plugs.

Any AM radios in close proximity will be blasted, though. At the voltages invoilved (20,000 and up), 5k or 10k of resistance doesn't mean a hill of beans to the spark, but it will help reduce radio spectrum RFI.

If you don't care about causing the interference, don't worry about it and run without the resistors. Keep in mind, though, that the resistor inside the SHORT cap is not removeable, only the one in the LONG cap is.

In practice, the resistor plugs and wires only REDUCE the amount of intereference, they will not eliminate it.

In a car the additional shielding of the steel body also helps attenuate the RFI,, but for us, with no metal shell, when we pull up next to a cage listening to talk radio, the static we generate can be is deafening.

IMHO, you won't notice much of a difference without the resistors, except if you had a bunch of gunk inside the cap in the first place, you will notice better running, but not because you removed the resistor, but because you cleaned the gunk!

HTH,

Randy

[John]

If they are listening to talk radio, it's probably rush limbaugh, or sean hannity anyway, so by all means, drown them out