NGK A7 spark plugs

[Dave Mann]

Has anybody any experience of using these spark plugs? A friends Ruby has them and it runs rough.

[Steve Jones]

An A7 would be quite an old plug, Dave. It was superseded by the AB7 some years ago so they might, simply, be past their best. The only difference is the size of the hex. It's Champion equivalent would be a D9 and they might be a bit 'hot' for a standard 7 engine. A6/AB6 or D16 probably more appropriate. However, today I've started to get my SWB Saloon ready to take to Morton. It's not been used properly since October 2020 when it wasn't running too well. Apart from keeping the battery charged up, I've not done much with it since then. It fired up pretty much first go even though it's got 19 month old petrol in it but it was still a bit 'rough'. Squirted a bit of light oil into the plug wells and looking at it ticking over I saw some bubbling and realised the Champion D16 plugs weren't sealing too well. Tightening them all made no difference but a change to a new set of AB6s transformed the thing. No bubbling so full compression. Maybe your friend's Ruby simply needs a new set of plugs.

Steve

[Charles P]

I've used A6, A7 and A8s on my Ulster.
It's happiest on A6s. I have about 3 boxes of NOS A6s that I'm using. They seem more tolerant of the two stroke that the car runs on than AB6s

Charles

[Derek Sheldon]

I spent several days trying to get a Ruby to run properly. It had New NKG7 plugs fitted. It wasn’t until I fitted a new set of Champion L86 plugs that it ran faultlessly. In my opinion chuck the NKG’s

[Charles P]

I spent several days trying to get a Ruby to run properly. It had New NKG7 plugs fitted. It wasn’t until I fitted a new set of Champion L86 plugs that it ran faultlessly. In my opinion chuck the NKG’s

Derek

The L86 is a 14mm plug and the NGK A6/7 (AB6/7) is an 18mm plug, so your Ruby must have had a really odd plug. 
Irrespective of make, changing the plugs for a new set is stage one fault finding in my book.

Charles

[John Cornforth]

Hi

The only time I had 14 mm plug related troubles was a one week holiday in Jersey when there was an unseasonably chilly Easter (easterly winds, hailstorms etc). The roads there aren't conducive to a good long blast, so the car never properly warmed up, and the plugs were prone to fouling and misfiring. The standard A7 ignition doesn't seem to have a lot of margin, and doesn't take kindly to carbon fouling.

Modern plugs don't seem to always respond to cleaning, and a new set is sometimes the only cure.

There have been reports in the past that NGK plugs are a popular target for counterfeiters, so this may have undeservedly detracted from their reputation.

[Dave Mann]

A return visit today with a set of new Champion D16 solved the problem.

[Derek Sheldon]

Just to clarify, NKG7HS was the faulty plugs , I replaced them with Champion L86c which is the replacement plug for the Champion L10

[Derek Sheldon]

Just to clarify, NKG7HS was the faulty plugs , I replaced them with Champion L86c which is the replacement plug for the Champion L10