SOHC.co.uk Forums > CB500/550

Plugs fouling at idle

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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:

--- Quote from: Johnwebley on April 23, 2024, 03:15:15 PM ---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,


--- End quote ---
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.

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