spark plugs

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spark plugs

Postby tonic » 08 Jun 2018, 18:46

Hi all
Been having trouble with sooty plugs, had mot done and the gas analyser read that it was actually running lean. I assumed it was running rich, can anyone tell me if i have the correct plugs. They are ngk bp6et the 3 pronged variety. thanks in advance. Tony
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Re: spark plugs

Postby sarran1955 » 08 Jun 2018, 18:52


What is the motor.. :?:


Help and advice on Aircooled engines here:
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Re: spark plugs

Postby silverbullet » 08 Jun 2018, 18:55

Best off asking in the Technical/mechanical sub-forum ;)

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Re: spark plugs

Postby tonic » 08 Jun 2018, 19:53

Hi engine is a 1.9 dg petrol 1989.
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Re: spark plugs

Postby tobydog » 08 Jun 2018, 20:07

Knowledge is power
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Re: spark plugs

Postby Mr Bean » 08 Jun 2018, 22:07

If I have it right your engine will be at normal running temperature at the time of the MOT test and the measurement will be made at a specified RPM. Assuming the vehicle passes then this could give some kind of indication that it is not running over rich. However if you check the plugs in an engine that has not been properly warmed up or maybe left ticking over for a while then I guess it is possible that the plugs will look sooty.

In the days of 405 line TV and trouser turn-ups - greasy Jeans not counted, we used to thrash the doo -da's out of our Cafe Racers and pull the plugs when still hot so as to determine if we had what we thought was the correct mixture i.e. beige to light brown. To be honest I don't think I have ever checked the plug colour on my somewhat more sedate 2.1 WBX high top but the interior of the exhaust tail pipe never never looses that ever so slightly sooty look. Maybe I am getting sloppy these days...
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Re: spark plugs

Postby 937carrera » 09 Jun 2018, 07:48

If the carb is badly adjusted it could be weak at idle and rich when at normal speeds. The MOT test for a T25 will be carried out at idle.

Do a search on the site for Pierburg and you'll get lots of hits, this seems a pretty decent read too

Before diving into your carb, I suggest you upload a photo of your plugs, see what other people think
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Re: spark plugs

Postby phinw » 09 Jun 2018, 07:52

tonic wrote:Hi engine is a 1.9 dg petrol 1989.

Yes, those wil do.
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