NGK iridium spark plugs

[uncle duke]

Hi fitted a set(4) iridium plugs in the s2r during the winter DCR8EIX used the bike & seemed fine but then after a couple of weeks it seemed to loose a bit of response & even missed a bit so I checked them & they were all very sooty put the old ones back DCPR8E & it's been fine ever since . admittedly it was colder weather while I had the iridium plugs fitted & the journey was only about 10miles but has anyone else had problems with the iridium plugs ?? Just checked the originals I put back in & the colour is spot on .any ideas ?
Roger

[rollo22]

Roger,

Found this

Older engines
Using a platinum or iridium spark plug in an older engine may lead to the fouling of the plug rather rapidly because the plug is too cold to burn off any excess fuel and oil that get into the combustion chambers of the engine. Burning off extra fuel and oil is what the hotter copper core spark plugs did very well.

Duncan

[Luddite]

When you fitted them, did you set them to the OE gap of 0.7 - 0.8mm? The iridium plugs have a narrower centre electrode and require a larger gap in order to generate a fat enough spark. If they are on OE gaps, try opening them out to 0.9 - 1.00mm and see if that makes any difference.

I've been running the same plugs as you, (with a 1mm gap), on my Evo for over three years with no problems.

Some more information here at posts #4 & #8: http://www.ukmonster.co.uk/monster/s...ad.php?t=54154

[Darren69]

I think maybe as Lud says it could be the gap or you could need a slightly hotter rated one, but if they work ok for him with the gap set wider then look at that first before putting in a hotter one.

[Flip]

Originally Posted by rollo22

Roger,

Found this

Older engines
Using a platinum or iridium spark plug in an older engine may lead to the fouling of the plug rather rapidly because the plug is too cold to burn off any excess fuel and oil that get into the combustion chambers of the engine. Burning off extra fuel and oil is what the hotter copper core spark plugs did very well.

Duncan

Yep I completely agree with that!!

In my experience (I’ve used them once in my carby 900) they didn’t get hot enough and went sooty pretty quickly- not to the point of causing it to run rough but I don’t think the larger gap Iridium plugs needs helps on older ignition systems either.

It may be better on fuel injected motors but personally I wouldn’t use them again.

[smiffyraf1]

yeah ive had the same experience with my 1000ds. fitted them thinking more expensive must be better. no ran like crap. fitted replacement originals and totally fine.

[jonzi]

I put iridium in my 796, changed the gap to what was recommended by Luddite in another thread, but still having problems with the bike starting when it's hot.

this thread has reminded me to buy some normal NGK ones.

[350TSS]

I read this somewhere - words to the effect - "Ducatis are wasted spark ignition - firing every crank turn and the marginal coils (on carbies) do not get enough time to recover before being fired again. If you add in a bigger plug gap the coil barely pushes out enough juice to jump the gap and when it does the spark is a bit later so the actual burn of the fuel commences later i.e. the actual ignition runs a bit retarded (the timing trigger says go but the conditions in the cylinder head determine when the spark actually jumps, low revs wide open throttle being the worst condition i.e high cylinder pressure and early in the advance curve so the spark fails and the engine fluffs).

The stick coils on wet bikes have an even lower output than carbie ones c20k volts but the ECU compensates for the lower spark ouput by reading ambient vs engine temperature, revs and throttle position and immediate throttle demand history ( I may be wrong on this last point) and almost instantaneously amends the timing to get the optimum burn rate in the cylinder".

Obviously a better solution if all the sensors, connectors and associated wiring and the ECU are in good condition but a right PITA if any are less than perfect or worse intermittently good.

Except for the last sentence, I think this was written by the NZ bloke who runs Fastbikegear and it was my justification for buying his expensive Hall effect ignition triggers that work off the central cam belt pulleys which obviously operate at half engine speed.

[jerry]

I have Iridium in my S4 , with the bigger gap they work well ,, but my old 1991 750ss did not like them and has standard NGK plugs plugs ,,the M750 2000 has Iridium and is fine ...
The 1997 one I bought last year also has Iridium plugs in .

I fit Denso Iridium plugs to all my bikes and have never had a problem with them. The Denso ones have a finer tip than the NGK Iridiums and I've always understood that the concentration of voltage at a fine point leads to easier spark generation, such that they can take advantage of a wider gap and produce a better flame. In my experience, fitting the Denso Iridiums is a very good way to get speedier starting, and they seem to last so much longer than fat-electrode plugs that the extra expense is fully justifiable.

Nick

[Flip]

Originally Posted by 350TSS

I read this somewhere - words to the effect - "Ducatis are wasted spark ignition - firing every crank turn and the marginal coils (on carbies) do not get enough time to recover before being fired again. If you add in a bigger plug gap the coil barely pushes out enough juice to jump the gap and when it does the spark is a bit later so the actual burn of the fuel commences later i.e. the actual ignition runs a bit retarded (the timing trigger says go but the conditions in the cylinder head determine when the spark actually jumps, low revs wide open throttle being the worst condition i.e high cylinder pressure and early in the advance curve so the spark fails and the engine fluffs).

I completely agree with you, that is pretty much what I’ve seen on my old carby 900 and I am sure I have read similar or the same as that- certainly’Ducati up North’ go on about the ignition and the early bikes generally weak electrics due mostly to the undersized cable used.

Which is why I have these little beauts ready to fit when Mrs Flip gives me a break in decorating

[Luddite]

Originally Posted by 350TSS

"...If you add in a bigger plug gap the coil barely pushes out enough juice to jump the gap...

I think that's true if you have larger gaps on standard plugs but, as I understand it, the narrower electrode on iridium plugs means less voltage is needed to jump any given gap. So the larger recommended gap shouldn't take any more voltage than with a standard copper plug.

This from http://www.sparkplugs.co.uk/iridium-spark-plugs/

"... The narrow diameter concentrates the electrical charge and therefore a much lower voltage is required to jump the spark gap. This is beneficial in several ways:
• A lower voltage is required, this reduces load on a vehicle's ignition system (less strain = less chance of failure)
• A larger gap can be supported without increasing load on the ignition system (Larger gap = larger spark = more efficient combustion)..."

[350TSS]

Luddite: I think someone is trying to sell more expensive iridium plugs - surely the coil delivers its designed voltage because that was what the designer of the coil and the manufacturer had a spec for.
The ability of the electric charge to jump the gap should be a function of the pressure in the cylinder, the density of the fuel mix in the combustion chamber, the time the coil has had to recover from the last discharge, the temperature of the cylinder head and the position on the prescribed advance curve and the cleanliness /conductivity of both sides of the gap.
The voltage at the side of the gap from which the spark starts to jump will be what the designer/ manufacturer specified regardless of the thickness of the electrode. This may or may not be enough to jump the gap depending on the circumstances above.
I suspect a bigger gap is harder to jump than a narrower one, think about striking the arc on a stick welder.

I also wonder if a long thin spark ignites the fuel better than a shorter thicker one.

You can tell I am a bit bored. Let's have a debate and we can all talk boxxocks about subjects we (particularly me) know hardly anything about

[Darren69]

You are best to stick with the oem plug spec then its seems, particularly on the older 2V carbies. But if Iridiums are better for cold starting on ie bikes like an S4 then I'm in. Let's debate!

[Mr Gazza]

I don't claim to know very much about electricity when it comes to all this high tension stuff, but I'm going to throw in a curved ball by way of livening the debate.

This comes from a lovely old boy I was priveledged to know, he lived to over a hundred and was a master of make do and mend, having survived some rather challenging times.

He told me about a trick they use to use on old (petrol) lorries with ageing coils and knackered spark plugs (probably two part plugs) To get a better spark they would cut the HT lead and bare back a bit of copper on each end, then thread each end into the holes in a shirt button and bend it back. So the bare ends are now a few mm apart. The spark then jumps the gap at the shirt button and this apparently makes a fatter spark at the plug... So how come? What's going on there?

You always remember these stories, and he illustrated it with a simple comment.. "You should have seen it with the bonnet up in the dark!". It leaves a mind picture..