[Mick Bailey]

Under some conditions the heat range of a plug can affect an engine's starting behaviour. If the insulator nose is not getting hot enough to burn off deposits, a layer of carbon (or partially burnt deposits) can form a conductive path between the central electrode and the plug body. It can be conductive enough to make cold starting very difficult, but when the engine is running it only marginally affects the spark intensity. I recently had exactly this problem with my own bike and it wasn't until I removed the plug after a run and set it up on my benchtop test rig that I observed the problem first-hand.

References to the presence of a plug resistor causing the voltage to be higher before jumping the gap isn't the case; unless current flows through a resistor there's no voltage drop across it. Basic Ohm's Law. The terminal voltage is the same whether the resistor is there or not. Prior to the gap breaking down there's no current flow, therefore no voltage drop. The presence of the resistor isn't a hurdle to overcome. If you have (say) a 20Kv supply and insert a resistor in series - even a high value - the voltage will still measure 20Kv if the meter is high enough impedance not to load the circuit.

[tooseevee]

     To finbullet and Mick Bailey:

            Excellent comments, both of you. Thank you.

             I'd just like to say first off that (A) none of the NGKs (many) that I used from May 2014 to June 2017 was in the engine long enough to get "old" to any degree at all. None of them ever "looked right" when pulled no matter how well I figured the carb was dialed in and I would throw another new one in and pray; (B) I experimented with gaps from .020" (Pete Snidal) up to .028" over those years (with the NGKs and the OEM coil) - no apparent difference. I never, ever came close to a cold, first thing in the morning, kick start; (C) when I installed the Pertronix last season I stuck with .028" and still got no cold kick starts with the Pertronix.

           I'm going to pull the Champion today both to just look at it (after 18 days) and to check the gap. I'll bet it's around 0.028" give or take.

            Now - a bottom line once and for all question:

             With the Pertronix and a non-resistor HT wire straight from  coil to plug, does it make any damn difference whatsoever To The Engine (I don't care about radios) whether I use a resistor or non-resistor plug?

               I don't think radios (car or otherwise) react like the old days to non-resistor ignition systems. Do they? And even so, do I care? No, I do not 

             

[Otto_Ing]

     To finbullet and Mick Bailey:

            Excellent comments, both of you. Thank you.

             I'd just like to say first off that (A) none of the NGKs (many) that I used from May 2014 to June 2017 was in the engine long enough to get "old" to any degree at all. None of them ever "looked right" when pulled no matter how well I figured the carb was dialed in and I would throw another new one in and pray; (B) I experimented with gaps from .020" (Pete Snidal) up to .028" over those years (with the NGKs and the OEM coil) - no apparent difference. I never, ever came close to a cold, first thing in the morning, kick start; (C) when I installed the Pertronix last season I stuck with .028" and still got no cold kick starts with the Pertronix.

           I'm going to pull the Champion today both to just look at it (after 18 days) and to check the gap. I'll bet it's around 0.028" give or take.

            Now - a bottom line once and for all question:

             With the Pertronix and a non-resistor HT wire straight from  coil to plug, does it make any damn difference whatsoever To The Engine (I don't care about radios) whether I use a resistor or non-resistor plug?

               I don't think radios (car or otherwise) react like the old days to non-resistor ignition systems. Do they? And even so, do I care? No, I do not 

             

I've found some good reading about it... someone who actually looked closer at what exactly happens.

http://www.ultralightnews.ca/articles/resistorcapsandplugs.htm

[Mick Bailey]

The noise that affects radio and TV is the same noise that can disrupt an electronic ignition system. It can cause misfiring, latching-up (where the processor logic sticks in a fixed state) or multiple triggers. The spark discharge is very abrupt and the edges of the waveform generate harmonics into the radio frequencies. The purpose of the resistor is twofold; it alters the time-factor of the discharge in slowing it down, resulting in a less-abrupt discharge over a longer duration (though with lower instantaneous energy). Also, the resistor is wire-wound and has an inductance and therefore impedance. This frequency-dependent aspect means that higher frequencies see a greater effective resistance than lower ones and this reduces the radio-frequency components.

IMHO, you should use either a resistor cap or a resistor plug with a solid-core wire. In fact, I don't like resistive HT leads at all due to the absence of any significant inductive component. 

[Otto_Ing]

The noise that affects radio and TV is the same noise that can disrupt an electronic ignition system. It can cause misfiring, latching-up (where the processor logic sticks in a fixed state) or multiple triggers. The spark discharge is very abrupt and the edges of the waveform generate harmonics into the radio frequencies. The purpose of the resistor is twofold; it alters the time-factor of the discharge in slowing it down, resulting in a less-abrupt discharge over a longer duration (though with lower instantaneous energy). Also, the resistor is wire-wound and has an inductance and therefore impedance. This frequency-dependent aspect means that higher frequencies see a greater effective resistance than lower ones and this reduces the radio-frequency components.

IMHO, you should use either a resistor cap or a resistor plug with a solid-core wire. In fact, I don't like resistive HT leads at all due to the absence of any significant inductive component.

That makes sense...but aren't the cap's and plugs using a ceramic resistor, where would the inductive component come from?

[elysianforest]

That makes sense...but aren't the cap's and plugs using a ceramic resistor, where would the inductive component come from?

I'm no spark plug expert, but if Mick's right about the resistor being wire wound you have your answer there. Some diagrams also show a spring involved which could also introduce inductance.

[heloego]

Well, awright! 

Seriously glad that worked out! Gotta give it a shot, see if it works on my '06. Curious whether the displacement and OEM ignition/condenser will have any effect on it.

[Mick Bailey]

Older designs used carbon composition resistors. These have a high pulse-handling capability but no significant inductance. Modern interference suppression resistors are specifically designed for automotive systems due to the increased need to reduce EMI in electronic-intensive vehicles. They're not bare windings and have a vitrified or other heat-resistant and insulating coating so look like a ceramic bar with end caps.

When present, the spring does introduce inductance. This is sometimes wound with stainless resistance wire and in conjunction with a composite (non-wirewound) resistor this provides an additional level of suppression.

At one time the only things needing protecting were the car's radio and domestic TVs and radios. Now you have extensive electronics on vehicles that need protection, plus phones, sat-nav and other stuff used in and around a vehicle.

[Ice]

 There is some other subtle factor here that I can't pin down.

 All of the HD's I've owned preferred Champion and Autolight mildly tolerated Bosh and NGK a bit less and absolutely disliked Nippon Denso plugs.
 My Iron Barrels like Champion then NGK.  My Asian bikes preferred Asian plugs. I have no theory as to why.

Some of my friends have nearly the same anecdotal experiences on this topic.

[Mick Bailey]

On my test rig I've observed the spark characteristics of quite a few plugs recently. For a given electrode configuration and gap (what may be called a 'standard' plug), there can be a difference in how the spark jumps the gap. This may account for how plugs from different manufacturers and of the same nominal rating and type behave in different engines.

My broad observation is;

1. Strong blue/white spark that jumps the gap in the same location.
2. Strong blue/white spark that may stay in the same location at low RPM, but at higher speeds moves around. This movement depending on whether the electrodes are parallel or angled.
3. Strong blue/white spark that is occasionally interspersed by a number of simultaneous weaker sparks, purple in colour, that occur in different locations.
4. Multi-stranded sparks that tend towards a purple colour that occur simultaneously at a number of locations across the electrode faces. No single spark.

I noticed on the 'scope that the plugs exhibiting the characteristics described in 3&4 generated more interference.

[tooseevee]

      This has ended up being an incredibly interesting thread - thank you to everybody who has commented. I chased this problem SO long and it was SO easy to solve.

        I can't explain for the life of me why I didn't do it sooner - like in 2014. We grow too soon old and too late smart 

       

[hpwaco]

Too soon old, too late smart!   My long departed 98 year old grandfathers comment on life.

[tooseevee]

     I've had many monkey wrenches thrown into my gears* this week, but I finally got around to pulling that Champion plug after 20 cold starts and warmups in the garage since June 23 and two (2) very short runs down the road (5 or 6 miles).

      The pictures aren't really great, but I'll just say this Champion looks Grrrrate! compared to the many NGKs I've pulled and replaced. The difference is amazing. I can't show valid pictures of the shitty looking NGKs that I've kept because they've all been cleaned to various degrees and aren't accurate illustrations of how shitty they ALL were when pulled out of the engine. To look at the NGKs, you would think that my carb was WAY out of dial-in which it is not.

         Also, this Champion has been running with exactly the same carb jets and settings (TM 32) as with the NGKs. No parameters of any kind are different. Only the plug change.

         This plug was 0.028" out of the box and so were two unused ones I checked. I'm leaving them there unless I get comments that make me believe I should change the gap.

           What looks like a "glob" of crap at the bend of the ground electrode is an illusion of the photo. It's just a very thin black coloration that almost looks like anodizing rather than a deposit. The actual plug coloring looks VERY good to me.

         * I wonder how many remember what a monkey wrench is without Googling it     

[hpwaco]

It appears that the NGK hot to cold numbers are reversed on tooseevees chart.

[Arizoni]

It appears that the NGK hot to cold numbers are reversed on tooseevees chart.

I believe your right.

With NGK plugs the lower the number, the hotter the plug.
The higher the number, the cooler the plug.

Champion is just the opposite.
The lower the number, the colder the plug.
The higher the number, the hotter the plug.

Borrowing 2CV's chart, he shows:

         NGK                   CHAMPION   

     HOT                B9ES                      RN2C
      to                  B8ES                      RN3C                   RN3C
      COLD             B7ES                      RN4C

It should be

         NGK                   CHAMPION   

     HOT                B7ES                      RN4C
      to                  B8ES                      RN3C
      COLD             B9ES                      RN2C