Plug of the Day

This NGK BPR7ES is new. I took the ’73 850 for a 40 minute run, mostly at around 1/8 to ¼ throttle on some good twisty roads. Towards the end of this ride is a longish hill, a mile or so, up which I held a steady half throttle (80 mph) before pulling in the clutch and holding the kill switch. I took these plugs out at the side of the road and fitted some alternate plugs to finish my ride home. It's taken me a long time to get the idle and off-idle running right, so I'm now moving on to the mid range (1/2 throttle). What looks like it could be a shadow on the insulator is, actually, a carbon "tide mark".




I know a plug chop of this type doesn’t give definitive results, but I think this plug looks quite a bit like the ones shown by forum member “click” in this, now closed, thread.

https://www.accessnorton.com/NortonCommando/spark-plugs-what-do-you-guys-think.27752/#post-419437

The consensus on click’s plugs was that they were about right, but someone with more experience might see something different about mine. One thing I don’t yet understand is the color change on the outer electrode. You can see in the pic above the very end of the outer electrode is a slightly different color (it's not just the light), is that what I’m looking for?

ggryder said:

This NGK BPR7ES is new. I took the ’73 850 for a 40 minute run, mostly at around 1/8 to ¼ throttle on some good twisty roads. Towards the end of this ride is a longish hill, a mile or so, up which I held a steady half throttle (80 mph) before pulling in the clutch and holding the kill switch. I took these plugs out at the side of the road and fitted some alternate plugs to finish my ride home. It's taken me a long time to get the idle and off-idle running right, so I'm now moving on to the mid range (1/2 throttle). What looks like it could be a shadow on the insulator is, actually, a carbon "tide mark".

I know a plug chop of this type doesn’t give definitive results, but I think this plug looks quite a bit like the ones shown by forum member “click” in this, now closed, thread.

https://www.accessnorton.com/NortonCommando/spark-plugs-what-do-you-guys-think.27752/#post-419437

The consensus on click’s plugs was that they were about right, but someone with more experience might see something different about mine. One thing I don’t yet understand is the color change on the outer electrode. You can see in the pic above the very end of the outer electrode is a slightly different color (it's not just the light), is that what I’m looking for?

Click to expand...

Looks fine to me.

With unleaded gas, you cannot use spark plug coloration to tune jetting.

Been that way since the inception of unleaded fuel. 50 years.

concours said:

With unleaded gas, you cannot use spark plug coloration to tune jetting.

Been that way since the inception of unleaded fuel. 50 years.

Click to expand...

Bob,
What is happening with unleaded gas as far as the plug reading goes?Is there a basic answer for this ?
At least you can see if both sides are reading the same,correct?
Thanks,Mike

Cannot get it to rev above 4000?
You have entered a different world of throttle slide cutaway needle jet, needle position etc.
We'll need information on any mods done to the engine, larger carbs, bigger inlet ports etc. Or it's almost impossible to diagnose over the internet.

YING said:

Bob,
What is happening with unleaded gas as far as the plug reading goes?Is there a basic answer for this ?
At least you can see if both sides are reading the same,correct?
Thanks,Mike

Click to expand...

The subtle differences in tuning do not change spark plug coloration. In order to see a difference, the change is dramatic.
With no offense intended, we are a group of old duffers who grew up when "reading a plug" was a common skill.

Those days left us (except for racers using LEADED gas) when
unleaded fuel was mandated for street use. (1-1-96 was the end date for leaded pump gas in the US, phased out beginning1974.)

When the air fuel mixture is rich(strong) enough to color a plug anything OTHER THAN BONE WHITE, it is waaaaay too rich.
The old guys trying to replicate what is shown in repair manual spark plug pictures from 1968 is a folly.

To summarize, if you are running UNLEADED PUMP GAS (this has NOTHING to do with ETHANOL/NON-ethanol) your spark plugs should be snow white.

Many people mistake the coloration from oil consumption as jetting evidence on these old engines.

That little bit of tan coloration on the top edge of the porcelain close to the electrode is fine as long as the motor is pulling strong from idle to whatever comfortable high RPM you run at. Unleaded pump gas does burn hot, but some color evidence can be achieved and still have a strong street engine. If you go too far to the White side, you may end up with a very weak top end. Depends on what you are tuning for and if you have a feel for the difference between a lean or rich tune. Some do most don't.

ggryder said:

This NGK BPR7ES is new. I took the ’73 850 for a 40 minute run, mostly at around 1/8 to ¼ throttle on some good twisty roads. Towards the end of this ride is a longish hill, a mile or so, up which I held a steady half throttle (80 mph) before pulling in the clutch and holding the kill switch. I took these plugs out at the side of the road and fitted some alternate plugs to finish my ride home. It's taken me a long time to get the idle and off-idle running right, so I'm now moving on to the mid range (1/2 throttle). What looks like it could be a shadow on the insulator is, actually, a carbon "tide mark".

I know a plug chop of this type doesn’t give definitive results, but I think this plug looks quite a bit like the ones shown by forum member “click” in this, now closed, thread.

https://www.accessnorton.com/NortonCommando/spark-plugs-what-do-you-guys-think.27752/#post-419437

One thing I don’t yet understand is the color change on the outer electrode. You can see in the pic above the very end of the outer electrode is a slightly different color (it's not just the light), is that what I’m looking for?

Click to expand...

If you are talking about the color on the strap, that is a good indicator of the proper plug heat range. You are looking to find that discoloration in the bend area of the strap. This is one of the few indicators that are left due to lead free fuel.

concours said:

The subtle differences in tuning do not change spark plug coloration. In order to see a difference, the change is dramatic.
With no offense intended, we are a group of old duffers who grew up when "reading a plug" was a common skill.

Those days left us (except for racers using LEADED gas) when
unleaded fuel was mandated for street use. (1-1-96 was the end date for leaded pump gas in the US, phased out beginning1974.)

When the air fuel mixture is rich(strong) enough to color a plug anything OTHER THAN BONE WHITE, it is waaaaay too rich.
The old guys trying to replicate what is shown in repair manual spark plug pictures from 1968 is a folly.

To summarize, if you are running UNLEADED PUMP GAS (this has NOTHING to do with ETHANOL/NON-ethanol) your spark plugs should be snow white.

Many people mistake the coloration from oil consumption as jetting evidence on these old engines.

Click to expand...

Thanks for the reply.Much appreciated
Mike

ggryder said:

This NGK BPR7ES is new. I took the ’73 850 for a 40 minute run, mostly at around 1/8 to ¼ throttle on some good twisty roads. Towards the end of this ride is a longish hill, a mile or so, up which I held a steady half throttle (80 mph) before pulling in the clutch and holding the kill switch. I took these plugs out at the side of the road and fitted some alternate plugs to finish my ride home. It's taken me a long time to get the idle and off-idle running right, so I'm now moving on to the mid range (1/2 throttle). What looks like it could be a shadow on the insulator is, actually, a carbon "tide mark".

I know a plug chop of this type doesn’t give definitive results, but I think this plug looks quite a bit like the ones shown by forum member “click” in this, now closed, thread.

https://www.accessnorton.com/NortonCommando/spark-plugs-what-do-you-guys-think.27752/#post-419437

The consensus on click’s plugs was that they were about right, but someone with more experience might see something different about mine. One thing I don’t yet understand is the color change on the outer electrode. You can see in the pic above the very end of the outer electrode is a slightly different color (it's not just the light), is that what I’m looking for?

Click to expand...

Why was that thread closed? I didn't see any bickering.

concours said:

Why was that thread closed? I didn't see any bickering.

Click to expand...

Was it an old thread ? If so I believe Jerry has closed them to save people replying thinking they are current threads

I read the plugs and exhaust exit color. Not sure if that means I'm old, or just have not a clue what I'm doing. lol

If I get grey or light tan at those two locations and the motor does not exhibit any faults anywhere in the power band, I figure I'm doing well enough. My exhaust tip looks light tan on pump gas for a couple thousand miles after a motor refresh, then starts to darken up. Now my plugs are showing on the darker side. The oil burning is indicated around the edge of the end of the plug threads. I don't think burning oil shows tan on the porcelain, but I could be wrong. I sure hope so, consistency being wrong all the time is important.

I use a colder Autolite plug than a BPR7ES.

Don't take my word for it....

https://www.rockettbrand.com/downloads/tech_bulletins/Tech-Tuning with Unleaded Gasoline.pdf





I remember the exhaust pipes on my 1968 Ford LSD 428 4V being light tan when running it hard.

Bernhard said:

Cannot get it to rev above 4000?
You have entered a different world of throttle slide cutaway needle jet, needle position etc.
We'll need information on any mods done to the engine, larger carbs, bigger inlet ports etc. Or it's almost impossible to diagnose over the internet.

Click to expand...

Bernhard,

Not sure what you mean by "cannot get it to rev above 4,000?". I'm currently interested in the settings as they affect half throttle running, and at half throttle, up hill, the bike was doing 80 mph (which is more than 4k rpm). Obviously it would have rev'd higher/gone faster at full throttle, but that's not what I'm working on. The bike is stock '73 850 but would not run well at small throttle openings, even when hot, without some choke. The carbs are original Mk 1s here are some of the things I tried:
Pilot Jet #25 (0.017") & drilled out to (0.020")
Throttle Slide 3.5, 3 & 2.5
Needle Jet 105, 106(used/worn) & 106(new)
Needle Position clip in top and middle groove.

What I have ended up with is the Pilot jet drilled out to 0.020", #2.5 slide , 106 needle jet and the needle clip in the middle groove. The bike now runs nicely, but I wondered if the plug, as shown in the original post might be indicating a dangerously weak mixture. It seems that the color of the insulator might not provide an indication, but what about the carbon tide mark half way down the insulator? or the fact that the side electrode is clean, with no soot. I think I remember Jim Comstock writing that if the soot is burnt of the electrode all the way back to the shell, then things are a bit on the hot side?

Bernhard said:

Cannot get it to rev above 4000?
You have entered a different world of throttle slide cutaway needle jet, needle position etc.
We'll need information on any mods done to the engine, larger carbs, bigger inlet ports etc. Or it's almost impossible to diagnose over the internet.

Click to expand...

Wotchu talkin' bout Willis?

concours said:

When the air fuel mixture is rich(strong) enough to color a plug anything OTHER THAN BONE WHITE, it is waaaaay too rich.
The old guys trying to replicate what is shown in repair manual spark plug pictures from 1968 is a folly.

To summarize, if you are running UNLEADED PUMP GAS (this has NOTHING to do with ETHANOL/NON-ethanol) your spark plugs should be snow white.

Click to expand...

So, what about the "tide mark" someway down the insulator where it turns dark, presumably due to carbon deposits? Presumably those same deposits would color the tip of the insulator? Are you saying that if the mixture is correct the tip of the insulator is hot enough to burn that carbon away and so it remains "bone white". If you see any color towards the tip of the insulator it is not hot enough due to an excessively rich mixture?
So is the tide mark a useful indicator? Seems it is telling us something?
And what about soot on the side electrode? Same thing?

robs ss said:

Wotchu talkin' bout Willis?

Click to expand...

Maybe the wrong site ?
A bad dream?
A tractor ?

ggryder said:

So, what about the "tide mark" someway down the insulator where it turns dark, presumably due to carbon deposits? Presumably those same deposits would color the tip of the insulator? Are you saying that if the mixture is correct the tip of the insulator is hot enough to burn that carbon away and so it remains "bone white". If you see any color towards the tip of the insulator it is not hot enough due to an excessively rich mixture?
So is the tide mark a useful indicator? Seems it is telling us something?
And what about soot on the side electrode? Same thing?

Click to expand...

I humbly fold my tent.
Nothing to see here.
Carry on.

concours said:

I humbly fold my tent.
Nothing to see here.
Carry on.

Click to expand...

I'm not disputing anything you have written here. You are no doubt right when you say, "The old guys trying to replicate what is shown in repair manual spark plug pictures from 1968 is a folly." However, various spark plug threads show noticeably different looking plugs and the differences probably do indicate something about the mixture even if it's only enough for ballpark tuning.