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Author Topic: spark plugs  (Read 3710 times)


  • Guest
Re: spark plugs
« Reply #15 on: November 21, 2006, 10:17:21 PM »
I'm running the stock BMW 5k caps and Bosch WR7DC (remember, I've got the post '85 unleaded model).
I'm using them 'cos I bought 2 x 6 packs at a really cheap clearance price from an auto parts shop that was closing down years ago, and I now have plugs to last me years.
My reasoning was thus, an extra 5k resistance, in a circuit that already has an infinite resistance gap at the plug, is negligible. When the plug gap arcs, the arc is considered a conductor so has its own resistance, and at the voltages impressed on that circuit, these resistances totaled are not insignificant though for all intents can be ignored and help with current limiting to reduce spiking which causes EMR (RF interference).  
Also, my car (an '87 Toyota Corolla) specifies resistor plugs as well as suppressor leads. These leads vary from 12k ohm from the longest lead, to 6k ohm for the shortest, and add to this the coil to distributor leads resistance of 12k ohm, can add up to a maximum circuit resistance of 29k ohm!!! My car has run to 250000km without any problems so far, and still on the original coil.
Try the NGK bold and adventurous!!!!



  • Guest
Re: spark plugs
« Reply #16 on: November 22, 2006, 07:46:09 AM »
Bob Roller, I have a guess about what the primary and secondary circuits are, but I'd rather not sound like an idiot so could you tell me in some detail what you are calling the primary and secondary circuits please (i.e. where should I place the probes of my voltmeter)?


Offline Semper Gumby

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Re: spark plugs
« Reply #17 on: November 22, 2006, 08:40:32 AM »
HI Clutch,

I was thinking the same thing so don't worry about sounding like an idiot. (It's too easy!)  I'm was just contemplating my lazyness at reading or searching the internet for just such a procedure.  Which leads on the Bosch Coils and which on the Dyna (I have older Andrews products coils on a CB400F).  Its nice on the Bosch coils - each post is numbered!  Dawgone electrons are so hard to see otherwise.  ;)

Here is some thing cool - Sparkplug crossreference chart:

Coil testing but not Bosch or Dyna:

Ah Duane Asherman's site with a really good (simple) picture of a coil.  Suddenly the fog starts to lift! Read this!!

« Last Edit: November 22, 2006, 11:44:44 AM by Semper_Gumby »
Bill Gould ?1980/03 R65 When at first you don't succeed....Moo!

Offline Bob_Roller

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Re: spark plugs
« Reply #18 on: November 22, 2006, 04:43:39 PM »
The primary circuit is the low voltage side, where the slide on electrical connectors go on, the secondary circuit is where the spark plug leads plug into. To check the primary remove both wires and place your multimeter leads on each of the terminals. To check the secondary circuit, remove the spark plug leads from the coil, then insert one lead from your multimeter into each outputs of the coil, make sure they go in far enough to touch the metal at the base of the cavity.
« Last Edit: November 22, 2006, 04:52:25 PM by Bob_Roller »
'81 R65
'82 R65 LS ?
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!

Offline Rob Valdez 79 R65

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Re: spark plugs
« Reply #19 on: November 22, 2006, 05:19:08 PM »
Scans from the NGK Non-Automotive Catalog 2005: