Plugs fouling at idle

[deltarider]

Here is a question the experts in the international forum wouldn't (or couldn't?) answer.
In particular CB500/550s are known to easily foul their sparkplugs at idle. What - in theory - would make these CB Fours idle better: gapping the electrodes 0,6mm or 0,7mm? Please substantiate your answer.

[Johnwebley]

I dispute this,

My 500 has no issue

In fact, I use a harder plug than reccomended, an 8 instead of a 7 ,

I have checked the tickover mixture, and my airscrews are turned out more than normal,

I also have Boyer ignition, and run the plug gaps at 33thou,



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[deltarider]

I dispute this,

My 500 has no issue

In fact, I use a harder plug than reccomended, an 8 instead of a 7 ,

I have checked the tickover mixture, and my airscrews are turned out more than normal,

I also have Boyer ignition, and run the plug gaps at 33thou,

Is that plug a D8ES, a D8ES-L or a D8EA? What is the position of your airscrews.

I myself have had D8ES-L plugs many times, recommended by mecs if you travelled at high speeds.
Nowadays - many years older - I run D7EA. I see no advantage in gaps over 0,7 mm. You can expect they will erode sooner.

[Johnwebley]

Actually, I run Denso x24ea-u

I believe that the are equivalent to  the D 8ea

A d7ea is normal for the 500

The 8s are for 400,750 etc



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[deltarider]

Originally in the book it was D7ES which wasn't a particular good plug. Dealers in Holland considered it OK for the break-in period, but advised later to use newcomer D8ES-L if you would ride the highways. The D8ES probably would have been to cold. You may say the D8ES-L with its tip that protruded just a tiny bit further, was in between the 7 and 8. Also Honda France advised them for the CB500/550 and called them auto-nettoyante (selfcleaning). BTW, the D8ES-L was/is used on a wide variety of bikes. I had them in my CB500 on all my travels in Europe, often at maintained high speeds. I wouldn't have felt comfortable with the 7, not when you, what happened more than once, were late to switch to reserve... So it depends on your riding, but if the D8EA is the new name for the D8ES-L, it's a good choice. If you don't cruise over 5000 rpm, you may consider the 7EA.

[Bryanj]

Delta, i disagree,
On the asvise of an ngk rep who was a well respected sidcar racer i used D7EV in my 500 that went all over the UK and to the Isle of Man regularly plus commuting 7 miles to work.
Never fouled, never failed yes nearly twice the price but well worth it  the =L was always sold as a "half grade"

[deltarider]

Delta, i disagree,
On the asvise of an ngk rep who was a well respected sidcar racer i used D7EV in my 500 that went all over the UK and to the Isle of Man regularly plus commuting 7 miles to work.
Never fouled, never failed yes nearly twice the price but well worth it  the =L was always sold as a "half grade"

NGK came with the D8ES-L for a reason. Other plugs that had a less protruding electrode, fouled. That problem needed to be adressed. In my documents, the D8ES-L was characterised by NGK as "Special Design". Although it's been interpreted by forum members as "half grade" I've not seen this confirmed by NGK as such, nor by Honda. As the D8ES-L indeed fouled less, it could be used by CB500/550 owners that had read in their Owner's Manual and I quote: [...]" if the motorcycle is going to be operated for extended periods at extremely high speeds and near maximum power in hot climates, the spark plugs should be changed to a colder heat range number." That the American EPA was somehow involved in the birth of the D8ES-L, is a story that so far comes from one member only in the international forum. I have seen no confirmation of that story yet. I mean: how about all the other markets that didn't have an EPA?
Back in the day, every owner of a CB500/550 on the European continent ran the D8ES-L plug. My personal experience was that this plug fouled no more than the D7ES did.
One of the best manuals I have, is the French one that was established in close participation with Honda France. On page 83 we read:
Bougies
La CB 500 est équipée de NGK D-7 ES alors que le modèle actuel (CB 500 K1) possède des bougies NGK D-8 ES-L qui ont la particularité d'être autonettoyantes. Il est conseillé de monter également ces bougies sur la CB 500.
In translation:
The CB 500 is equipped with NGK D-7 ES while the current model (CB 500 K1) has NGK D-8 ES-L spark plugs which have the particularity of being self-cleaning. It is recommended to also fit these spark plugs on the CB 500.

And that's what most of us did.

I'm sorry I cannot comment on experiences/reviews which may be biased by free handouts. Untill I have more information, I consider them anecdotal.

 

[florence]

On my 500, I have D7EA and it ticks over perfectly, they do not foul.  Good response in all rev ranges, hot and cold.

Perhaps you should look at ignition timing and carbs rather than plugs.

[Bryanj]

The fact that the L was a half grade came from the same reptat suggested d7ev to me, and that man knew how to read plugs

[McCabe-Thiele (Ted)]

This is starting to read like "Plug-gate".

[K2-K6]

The fact that the L was a half grade came from the same reptat suggested d7ev to me, and that man knew how to read plugs

Thats noted on some published charts too .... the -L designation.

https://www.ngk.com/ngk-spark-plug-numbering-systems this lists that design element, although note that they have a statement of NOT being NGK USA official scource.

The listed data looks comprehensive though.

[deltarider]

Aha, that is valuable information. I had not seen this half-grade mentioned before. In Holland the general advice was to have the D8ES-L. Let me put it like this: if the D8ES-L fouled, than a "7" also did.
Now that we're older  and also have a lower national speed limit than back then, both the 7 and the D8ES-L can be used no prob.
I am curious if the D8EA is identical with the D8ES-L and if the D7EA also has a tip that protrudes just a fraction more than the D7ES. I have tried to see the difference myself, but I'm afraid the difference is minor and... older eyes don't help either.

[Johnwebley]

Back in the 80s

I also used Champion A8Y


Definitely a  projecting nose plug,

The bike ran well, but they became difficult to get

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[K2-K6]

Not owning a 500, I've not that specific experience to offer.

A big BUT though, genuinely I've never had problems with plug "fouling" on four stroke engines, that's across all bikes and cars I've looked after since early 1970s.

Another observation, the Boyer ignition is very, very competent in it's delivery. I've no problem working with the std system, believing it to be mechanically almost peerless in it's design, application and component specification .... the Boyer i can see by comparison does offer tangible benefits if that's chosen by the owner though.
Among those benefit appears the ability to fire more adverse mixture range more of the time with exceptional repeatability.  This seems to support a more optimum idle mixture that may give benefit in any residual unburnt component/fuel that may be affecting the fouling determination this topic is about.

Very loosely, NGK plug heat range on these engines could be approximated to continuous load under wider throttle for extended periods of time.
 A 7 giving ROUGHLY decent coverage for 7000 rpm running.
Likewise, an 8 for predominately covering an 8000 rpm consistent load type riding. Etc, etc
Basically its a balance of number of actuation per minute against heat clearance from the engine, ambient air temp also playing a part in air cooled motors too.

[florence]

I agree completely which is why I was asking if the fouling might have another cause, nothing to do with plugs.