ULP and spark plugs

PostPost by: Terry Posma » Tue Oct 04, 2005 12:17 pm

I have posted this question before without a result. Better luck this time.

Has anyone had previous experience and/or know of the reason why when plugs are cold and foul (in a situation like heavy traffic or idling while working on the car) no amount of cleaning will get them right again?

Put in a new set of plugs and you have good spark again.

This did not appear to be such a problem with leaded petrol and appears to happen with all makes and heat ranges of plugs. Car is a 130/5 with a good motor.

Terry.
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PostPost by: types26/36 » Tue Oct 04, 2005 1:16 pm

Sorry I cant answer that question but I suspect the plugs are just not clean, in days gone by when re-gapping plugs was standard practice cleaning plugs was done on a "sand blaster"
I have not seen a sand blaster in years and I doubt the mechanics of today have ever seen one.........thats progress! :roll:
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PostPost by: type26owner » Tue Oct 04, 2005 1:59 pm

Terry,
Fouling spark plugs are an indicator that something else is amiss or the plug is just too cold. Fouled plugs will self-clean in the engine if they can heat up enough. They are actually a heat exchanger afterall. The carbon will sublimate directly into CO if there is oxygen and enough heat to drive the reaction. A properly prepared engine should be able to idle for many thousands of hours without fouling the spark plug.

Cheer up because almost everyone is in the same picklejar. Unless you've corrected the factory derived problems on your own. The fuel back then and the thermodynamic solution for it are for a time that's gone. The fuels today are being made to be less volatile to reduce pollution. The measure of this is called the Reid Vapor Pressure. If the ULP is being lowered and approaching 7psi then alarm bells should be ringing there. That stuff is trouble for a carbureted engine to consume.
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PostPost by: M100 » Tue Oct 04, 2005 6:36 pm

Ditto on the fact you probably have too cold a plug. The modern hot plugs seem much more tolerant to extended high power running than in the past where you could easily end up with melted electrodes.

What make and grade of plugs are you using?

While i've sandblasted plugs in the past the current wisdom from the plug manufacturers is don't as it rounds off the plug electrodes which somehow affects the spark quality. How this is a problem i'm not sure but a curved surface will get to a larger voltage before it sparks whereas a sharp cornered electrode will spark earlier. Maybe the spark duration is longer with a sharp electrode.

In the UK the fuel volatility coming out of the refineries step changes around the end of October and reverts to summer fuel around April. What the precise difference in volatility actually is is anyones guess!
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PostPost by: twincamman » Wed Oct 05, 2005 2:09 am

I have used brake or carb cleaner with a high degree of success to clean spark plugs ---sand blasting is not recommended ----introduction of sand particles into the cylinders -----ed
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PostPost by: tdafforn » Thu Oct 06, 2005 11:55 am

I'm in the same situation...
In my case Some of it could be oil blow-by, my +2 is on 67K miles old and the twinc hasn't been molested yet (appart from a valve job on the head).
I guess I may try other plugs
Cheers
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PostPost by: stuartgb100 » Thu Oct 06, 2005 1:26 pm

FWIW,
On my Sprint, the plugs were N7Y's.
Whatever I tried, they were at best a light grey.
Now trying NGK BP6's (I think an N9Y equivalent) which are a hotter plug.

I now have much better colour. The move to a hotter plug seems the cure.

Regards.
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PostPost by: Terry Posma » Fri Oct 07, 2005 1:19 pm

Thanks for the all the input.

Currently have NGK BP6s. Have been advised to try BP5s or NGK Iridium in the same heat range. I will try the later next week and report back unless someone has already had a bad experience with them.

I have also been told not to sand blast due to the sand in the cylinder problem.

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