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[Scalyback]

when you are about to hit "post reply", select all the text and copy it first.



If the board then tried to looses your post, then just sign in, hit reply again, and then paste it all back in... YAY!



Maybe some body nice at

[Scalyback]

Well that went wrong. I meant somebody at Hitchcock's, please make logged in time somewhat longer? Thanks !

[nigelphoto]

For plug fouling answers take a look at this other Thread "EFI Idle' . It seems to have wandered a bit 'off topic' and is now all about plug fouling . . . . .

[jefrs]

"EFI Idle" was an old thread and has gone a bit sideways too, partly my fault, oops



Imo best bet for sooty plug is ditch the plug ('cos after a while they become uncleanable) and fit a new one then take it for a good burn up to decoke it (Redex in tank optional). If it is slow town traffic as I suspect causing the plug to foul then one that runs hotter will have better self-cleaning. Once they start fouling they just make matters worse. By hot plug I mean one with less thermal insulation. I can never figure out whether the makers say 'hotter' when they mean one for a hotter engine or they mean a plug that lets its electrode get hotter in a cooler engine. The there's 'hard' and 'soft'. The only way I can tell is by looking at them in ye shoppe of parts.

[nigelphoto]

Jeff - for 'heat range' explanation you can't get better than this http://www.ngksparkplugs.com/about-ngk/ ... lug-basics. Basically, the higher the rpm/load/compression the colder you need the plug heat range and conversely if you have a slow revving, plodding load lugging engine (ours!) then you need a 'hotter' running plug. NGK numbering runs the 'wrong way' so larger numbers indicate colder running, whereas all others larger numbers mean hotter running. For EFI engine NGK correct heat range is 6 and those damn Bosch its 6,7 Hope thats all OK

[PeteF]

Jefrs, what do you mean by uncleanable? I've got plugs back to life which have been completely caked and clogged. A brass brush and a fine pick does the job.
The plug in my side valve B&S lawnmower engine has been in there for 20 years and it's pretty well clogged up at every service but always cleans up to fight another year. The Bullet plug has been in for 20K and has endured all my attempts at tuning, often getting pretty sooty in the process. That always cleans up OK.

[jefrs]

PeteF - without getting too technical (I hope), a spark originates below the surface of the electrode after generating an electrical charge hot spot at the surface. When the spark jumps the gap it burns in to the electrode several molecules deep. Doing that will migrate the crud, the carbon, within the electrode eventually poisoning it beyond the capability of the wire brush. Cations and anions. There's a lot of energy in that little spark, it can rearrange atoms and vaporise metal. Also accounts for why the earthy electrode outside loses metal and gets thinner after prolonged use, the metal is quite literally being ionised and thrown off. This really only affects badly fouled plugs where the crud has been burnt in. If your bike is running reasonably cleanly you have nothing to worry about and will get many, many miles out of the plug. Carry on using the suede brush

[PeteF]

I know all that Jefrs but that's not what you said.
"best bet for sooty plug is ditch the plug"
In practical terms Sudburys is having problems with (probably) his mixture setting. Telling him to ditch the plug if it gets sooty is not very helpful. I repeat, I have cleaned up very dirty plugs year after year and they keep going with no loss of electrode metal.
I have no doubt your science is correct but in my experience plugs do not fail as regularly as you suggest.

[Presto]

There’s a fair bit of mis-information in this thread – no need for it, most of this stuff is on the NGK web-site – no need either for ‘super science’ to overwhelm us!



A spark plug’s ability to transfer heat determines its heat range. The heat range of spark plugs is classified either as ‘hot’ or ‘cold’ (or, as some prefer, as ‘soft’ or ‘hard’: HOT = SOFT; COLD = HARD.)



With N.K.G plugs the identification is that a higher number indicates a harder (or colder) plug. (This sequence is reversed with Champion plugs, so that a lower number indicates a harder grade of plug.)



A HOT (or soft) plug typically has a longer and thinner tip insulator, with more ceramic tip exposed to combustion heat and less in contact with the plug body. This arrangement restricts heat dissipation and consequence loss of heat from the plug tip, meaning that the plug runs at a higher temperature.



A COLD (or hard) plug has typically less of the tip exposed and more in contact with the plug body; heat is dissipated more efficiently, allowing the plug to run cooler.



One main function of a spark plug is to transfer heat from the combustion chamber. The ceramic insulator disperses about 4% of the heat generated (the ridges on the insulator are not for cooling but to reduce the risk of electrical current ‘tracking’). Approximately 90% of heat dispersed through the plug is transferred through the thread and washer, with approximately 40% of total heat transference through the plug washer itself (correct fitting and tightening of the plug is important).



The ideal operating temperature of the central electrode is between 400° and 800°c. If the plug tip fails to reach this working temperature it is liable to become contaminated. Carbon and/or fuel/oil are liable to gather on the plug tip leading to an engine misfiring. The electrical current, that normally generates the spark, is ‘lazy’, taking the most readily available route to earth. A fouled plug gives the current an escape route, allowing the current to ‘track’ through the debris on the insulator tip before reaching the electrodes. In a misfiring engine the plug will tend to lose heat, through the leakage of current, this will, in turn, inhibit the ability of the plug to self-clean, and create a vicious circle of failure.

[jefrs]

PeteF - you asked why I said a plug becomes uncleanable. I explained how they can become contaminated.

My recommendation to ditch the plug is when they reach that stage and keep missing. I think we have different concepts of 'very sooty', the iridium that came out of mine was caked in the stuff and missing very badly; the electrode on those is like a pin head. Cleaning it thoroughly brought it back to life but not 100%, it would still cough. Replacing it with a 'standard' BPR6ES stopped it missing altogether, plugs are not expensive..