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mikeracha

Spark Plug Caps - Resistor or Non-Resistor?

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Or don't worry about it. After my commute from hell with my spark plug cap coming off the plug twice, I was poking around and tried to figure out if it matters about resistor or non-resistor plug caps. I run Champion or NGK non-resistor plugs. Does it matter enough to worry about having a resistor Vs. resistor-free plug cap? 

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Stickey (2 ed., pg. 28) recommends a red rubber waterproof NGK 5K ohms resistor type (LB05EMH).

 

WW

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Resistor type for electronic ignition.

Non-resistor for points ignition.

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>>Resistor type for electronic ignition.
>>Non-resistor for points ignition.

 

What he said and avoid spark plug wires that don't have a stranded copper wire core in either case.  That carbon impregnated nylon crap is not the ticket for metal scooters.

 

The older machines tend to lose magnetism from the flywheel magnets and the original coils grow weak.  Probably not many stock coils in Lambrettas any longer, but the magnetism problem is for real.  Flywheels can be remagnetized by someone with the proper equipment.  SF Scooter Centre can do this.  The spark should be fat and blue and make a loud "crack" sound. 

 

You can still get generic spark plug caps at some auto parts stores.  They need the little threaded tip that comes with a new spark plug.  Cut away 1/2" of insulation from the spark plug wire, solder the wire strands to the the metal clip and slide the rubber boot over it.  I drill a small hole in the clip and run the wire strands through it and bend them back flush along the back of the clip and then solder.

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Non resistors also play merry hell on certain radio's and computer equipment, especialy the ones that are near flashing blue lights:)

 

The ngk ones seem to be the best, they seal up nice and tight against water getting in.

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Did some googling and came up with the following.  I've always kind of had an understanding, but I think I get it a bit more now.

 

Long read, but good info here:

 

http://www.motorcycleproject.com/motorcycle/text/plugwiretech.html

 

Upjettr gave the Cliff Notes version, but the above explains the why.

 

If you run a CDI ignition, you should probably have some kind of resistor from the coil to the spark plug.  This helps lengthen the life of the CDI.  There are 3 ways to add a resistor, usually 5KOhms per item:

 

1. Silicone plug wire (15 Kohms per meter)

2. Resistor cap

3, Resistor plug

 

Any one of these components will add the 5KOhm resistance needed.  On a scooter you are looking at about 1/3 of meter of silicone wire, so 5KOhms.  If you add more than one of the 3 items, you are adding 5KOhms at a time.  For example, if you run a resistor cap and a resistor plug, you are up to 10KOhms.  Train Driver obviously needs this much resistance so that his fancy speedo works.

 

Copper core wires offer no resistance.

 

How to check your resistance: http://www.powerdynamo.biz/eng/info/resistance.htm

 

Mike

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On 6/19/2014 at 3:52 PM, wihr said:

Stickey (2 ed., pg. 28) recommends a red rubber waterproof NGK 5K ohms resistor type (LB05EMH).

 

WW

THANK YOU!!

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