Plug Choice / Gap: G15-CS

Hi everyone:

With a Lucas K2F on my G15, I have been running NGK plugs gapped at .020-.022" per my owner's manual. (Copper-core wires and "lodge/KLG" type caps that have always been on it...) Is this gap too small? I've had two plugs die recently, now that the bike's running pretty well otherwise, I wondered if that seemingly-small gap had anything to do with it.

A bit strange in that earlier norton literature shows magneto equiped NHT plug gap to be .015" (BSA A10 being .014"). This is mainly for ease of starting at kicking speed.
Points/coil is entirely different and literature needs to be scrutinized or your K2F bike will start and maybe idle poorly.
Plugs are cleaned by the heat of combustion and fuel mixture ratio has the biggest control of keeping the plugs over 900deg for cleaning...

dynodave said:

A bit strange in that earlier norton literature shows magneto equiped NHT plug gap to be .015" (BSA A10 being .014"). This is mainly for ease of starting at kicking speed.
Points/coil is entirely different and literature needs to be scrutinized or your K2F bike will start poorly.
Plugs are cleaned by the heat of combustion and fuel mixture ratio has the biggest control of keeping the plugs over 900deg for cleaning...

Click to expand...

That is interesting. I originally had gapped at .015 due to having seen that spec somewhere. Then I looked in my copy of the original Norton manual and it said .020-.022 for all heavyweight twins. Figured the .015 gap was too small and might have killed my plugs.


(I was most wondering if there was a need to gap differently with modern plug choices compared to what's in old literature...)

So you think that .015 spec is the way to go? I wonder why I am killing plugs here...thought it was just fouling but after cleaning, two of them still won't spark.

Also of note, I have NGK B7ES in there, based on what previous owner used, but the Norton Owners site recommends BP7ES. I should try those, I guess, but my gap question still remains...

Also, high comp pistons (poss dunstall per original owner...) with mag timed to 28, for whatever change that makes. Comp test warm is ~150psi both sides

Other than fouling because you forgot to turn OFF the choke, if you ever foul a plug...your engine is sick.
Fixing the carbs is highly technical and without a dyno tuning is usually has the sophistication of a hand grenade. Foul the plugs or burn the pistons are a hint you are off the mark.
I have never bought plugs. People give their bad plugs to me. I run them in my bike until clean which is usually one hard blast up the highway.
I cringe at what I sometimes hear on the NOC forum...and here too!

Well, lacking any baseline on the engine (and much experience with Nortons at all, or internal.combustion in general compared to most of you here) I have been keeping a rich idle mix in an attempt to be on the safe/easier-starting side until I can tune them better...but I don't think fouling has actually been my issue at all, just new plugs that fail to fire after a short running time.

Are both plugs failing, or only on one side?

If one side, likely a mixture problem.

Both sides, could be weak magnets in the magneto.

Slick

Mike,

have you tested your magneto at all? K2F's and other magnetos have a limited life span. One thinks they awill last forever, unfortunately they won't. Once rebuilt and re-magnetisized, they are reliable for the next 20 years though. If you rule out the magneto, please check resistance of your HT chords and plug caps. These components will not last forever either. Maybe you have a HT leak somewhere?

-Knut

AgentX said:

just new plugs that fail to fire after a short running time.

Click to expand...

I am confused? what does this mean?
Do you check from the plug connection to the tip of the electrode for a continuity connection (zero ohms) ? Or has the internal connection broken open and shows infinity ohms? That's VERY RARE.
I own one of these and have it tagged as a sample to use for demonstrations to have people trouble shoot this rare but known problem.
Carbon and combustion byproducts coating the porcelain usually get deposited if the temp of combustion is to low (RICH mixture).
IMO rich starting should come from tickling/ flooding and not running idle adjustment, which is more than cold enough for the plugs.

dynodave said:

I am confused? what does this mean?.

Click to expand...

It means the plug won't fire after being cleaned, whereas another one of the same type will fire. I am checking with the multimeter now...as I said, fairly new to internal combustion engines and never had this kind of issue before, so I was using what basic logic I could, however flawed.

Mag rebuilt in 2015 or 2106 but not used since then (short test rides excepted, only one or two over a mile or two) and other plugs fire fine...


The one I was recently having trouble with shows continuity with .5 reading on the 200 ohm scale. One that's firing shows .3. Very strange.

The problem stayed with the plug regardless of which side's lead I plugged it into, which further made me think the plug itself had failed. But the failures both originally occurred on the left side.

The boot of the left plug cap does have a crack now that I look closely. I just fit it to a new wire yesterday.

AgentX said:

fairly new to internal combustion engines

Click to expand...

I am always challanged with IC engines. As I have learned beginning at 15 years old over the years since starting to "play" with them before I started in college (1969). My first experience was with a friends Alfa Romeo Guiletta sprint veloce we worked on...lots of fun.
Even at 20 I could not keep my 70 commando roadster on the road between vietnam tours.
Internal combustion engines are covered by a HUGE field of science, physics and very wide variety of engineering sub disciplines.

Plugs have a hi voltage feed from the source and voltage is normally expected to jump the gap in the form of plasma (called spark). The voltage sometimes is shunted by the conductive deposits on the porcelin which is an undesired path for the kernel of electrical energy. A bad plug with an internal break are very problematic. .2 or .3 ohms with a multimeter are functionally twins at DC low voltage and are OK. Yet at 6KV typical gap voltage(low cylinder pressure = idle) and tremendious DVDT rise time they react differently with the plug coating competing with fuel/air as the discharge path.
The extended tip plug BP6 or 7 may stay cleaner and more in the flame path to keep it warmer and cleaner at low power settings.

Yep, I think the ohm readings prove my problem is elsewhere...guess I didn't get the right parts clean. That said, if they're not showing resistance, why would they not fire, when other plugs will on the same wire/cap/mag position? I'm mystified.

Got two new P style plugs here now...any recommendations for the gap? .015, 0.020, or other?

I will get new plug caps, too.

Thanks again for all the assistance.

-Mike

If it was me, gap would be THE SAME AS BEFORE.
If new plugs fixes it, then the ceramic coating is proved as the problem.
I would ...next step... reduce plug to .015... do run test.
Only change plug caps as a separate step..after a run test.

Now the beginning of carb settings corrections

Will do...thx.

After a short test run, they were both a little sooty (too be expected, as it was 5 min at mid-speed), but the LH seemed a little wet and the RH very dry...

Main test results?
1. RH fire yes/no LH fire yes/no
Bonus trouble shooting Compare old plugs to above new plugs. Was previous failed plug from L or R

LH oil wet? fuel wet?..... Fuel dries out, oil does not...
Always evaluate as amount of throttle opening and load on engine. How much cylinder pressure?
RPM is much less relevant...

Mike,

Your problem seems to be related to the gas mixture (or oil contamination). However, checking the HT leads at the magneto end may be an assurance. Copper is known to corrode, and Cu salts are very good leads. Sparks will always seek the path of least resistance.

One other tip is testing your plugs in the dark and possibly have another observer nearby. If your magneto is in good shape, the sparks should be clearly visible at each plug, even if they jump at the insulator.

-Knut

Ok, so I went for a good long hour-plus ride. Missed all your messages in the meantime; they're much appreciated.

Based on the unassailable fact that the idle was overall too rich, I did some adjusting in a parking lot once it was warmed up. (Part of the reason it was overly rich was because my previous fueling problems had left it running lean much of the time, so when I set the idle mix, it wasn't against the proper fuel level in the carb...)

Both air screws are now backed out 1 and 1/2 turns...the jets, however, are 25s vice the spec'd 20s. (again, part of the overall lean mix from before...can swap the 20s back in now...)

It ran much better. I couldn't get it to idle properly under 1400 RPM because it was so rich; now it idled fine around 1100.

video-1588536323 by Mick Doul, on Flickr

I did not do a cylinder-by-cylinder tuning out on the road, but was pleased that this seemed to bring things back into normal



That said, I had other issues. At one point, RPMs started to raise on their own, and I turned on the reserve petcock, which calmed it down. But I had filled up yesterday and shouldn't have needed to be on reserve...plus I was able to turn it off later and it was fine again. So there's still something restricting fueling here. (Or it was another cable issue, but I checked that and it seemed OK...)

Got back and the plugs didn't match, though neither was dirty compared to before. The RH cylinder was a light tan insulator and no soot to speak of, save a little on the rim of the plug which wiped right away.

The LH was a much darker insulator with a little soot on it and a little more on the rim, just like the RH had. I'm fine attributing this to a need to tune each mix individually now. Sound right? I know the carbs are going to be a little off of each other.

It didn't want to start again when I put the plugs back in, either. I had wire-brushed them a little but not given a detailed clean. Both showed massive sparks from their respective leads. (Somewhat to Knut's point...) I'm not suspecting the magneto at all. It's shocked me once or twice and compared to my Enfield with a boyer and coil, it feels like a defibrillator...

Thanks again for your help and patience...I'm learning gradually.

Also of note in the video...you can hear the RH pipe (with the healthy plug) sound very "warbly" on overrun. (Harley-esque, I assume due to the open headers.) Is that an indicator of anything with the mix? I've only noticed it when the bike was set leaner than it had been in the recent past.