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Spark Plugs
#1
I have a 7 Special with a relatively tuned engine.
I'm using NGK B6H  S plugs, but after about 15 minutes it drops to two or less. On removal they are wet with fuel.
Do I need different plugs, or are my gaps wrong. John Wallace 07770 410 010


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#2
(13-06-2018, 02:09 PM)wallacelondon1@btinternet.com Wrote: I have a 7 Special with a relatively tuned engine.
I'm using NGK B6H  S plugs, but after about 15 minutes it drops to two or less. On removal they are wet with fuel.
Do I need different plugs, or are my gaps wrong. John Wallace 07770 410 010

Hi John,

A little more information helps diagnose what's going on - the head, carbs and ignition details or a photo might help here?

B6HS are 14mm short reach plugs so I'm guessing you've one of the later cast iron heads? According to my information they should work in that head and normal gaps of 20 to 25 thou should be fine if your coil is working. Have you tried swopping them between cylinders and is it always the same pots that foul? Are you sure it's fuel that's fouling them or oil and then unburnt fuel? B5HS are a little hotter and could help IF you're oily.

Dave
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#3
As Dave says it could be oil and I agree with his suggestions, to my mind it sounds highly likely that you are running too rich and fouling the plugs, extremely common with specials that are fitted with SU carbs and the wrong needle.
Location: Auckland NZ
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#4
I'm relatively new to Sevens but have had other cars(real Minis) and tuned Velocettes and Nortons. Not uncommon was the obvious desire for more power, so a larger carb was fitted. In Minis, putting a larger SU on often resulted in less power, more fuel consumption and fouled plugs. I would ask about the history of the build such as did this start right after the build, or was it running OK before? As well, specs are always helpful and where the fouling is occurring...idle, mid range, top end.

Erich in Seattle
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#5
NGK ship all plugs at 33 thou (IIRC) unless specifically stated on the box. [Source NGK home website technical section]

Could the gaps bee too large?
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#6
Years ago I suffered from oiled plugs and I tried every grade of 14mm Bosch and NGK plug imaginable.

Personally I would get one of the Ricardo aluminium cylinder heads with 18mm plugs, these are much less prone to oiling up.  You should also gain a few useful horsepower and get better mpg.   Money well spent!
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#7
I have seen advertised on eBay things called stilts which in effect are metal threaded tubes which lift the plugs up. The manafacturers claim they stop plugs oiling up. I have no expereance of using them however and do not know how effective they are.

John Mason
Running a Seven on a shoe string budget.
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#8
John, the stilts would have a dreadful effect on flame travel wouldn't they? I always feel it is better to fix the actual problem rather than introduce a crutch.
Location: Auckland NZ
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#9
(14-06-2018, 08:26 PM)Ian Williams pid= Wrote:John, the stilts would have a dreadful effect on flame travel wouldn't they? I always feel it is better to fix the actual problem rather than introduce a crutch.

A much better solution was to put a 'jumper gap ' at the high tension connection to the plug - a short strip of red fibre on each plug if I remember  - very colourful at night . Smile Smile Smile

Cheers, Tony.
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