Forum

[Presto]

There’s something very wrong if an iridium plug comes out heavily caked with carbon. NGK suggest a working life of up to 120,000 miles, the fact that these plugs in some of our bikes are failing after less than 100 miles points to something major that’s going wrong!



They also recommend that no attempt is made to adjust the gap on Iridium plugs. There is a risk that the very brittle central iridium electrode may fracture and, in use, fall into the cylinder. The plug gap is pre-set by the factory and, due to the efficiency of the Iridium plug, the factory-set gap will be suitable for virtually all applications. The same risk of the tip breaking also applies to cleaning iridium plugs.

[PeteF]

I didn't know we were talking about iridium plugs (Sudburys didn't seem to be)
I can see that it would be very difficult to clean an iridium plug which is one of the reasons I use conventional ones.

[Presto]

Fair comment PeteF - point taken. I agree, conventional type plugs can be cleaned and cleaned, at least that's what I've done with them for 50 odd years

[Dennis C]

Just a word of caution if using a hotter plug, please be aware that a hot spot is created around the plug when it fires, the hotter the plug the hotter the initial flame this can and does in some case's melt a hole in the piston. I have now seen three pistons melted in this way. Someone will now say I am wrong of course.

[Presto]

No Dennis, I think you are right to flag up that risk. With that in mind I added at the end of my first comments on this thread with a warning - 'Keep an eye on the plug after making the change, just to be sure it’s not too "soft".'

[jefrs]

As Presto explained, once a plug does get fouled the spark takes the lazy option to earth. That's what has happened to Sudburys, and my iridium (and my OEM Bosch-India but that was due to poor connection to HT cap). The iridium electrode is the size of a pin head which means less area to get fouled, so if that tiny area gets fouled, it can't find a clean spot to spark from and does not self-clean, for the reasons Presto pointed out. It gets fouled because the engine is running rich but the engine is running rich because the plug is fouled and missing so the remaining unburnt fuel which didn't get expelled clung to the combustion chamber and gets added to the next cycle, and so on. Now this may be a bit of an RE problem, afterall they do have Twin-Spark models for precisely this reason.



So what's to do? There are two problems. One to clean the now-carbonised engine. One to prevent it happening again. You could fit a hotter plug to self-clean better in a cold lazy town engine, which doesn't suit one ridden more enthusiastically, nor does it clean up the motor. Me, I've put a BPR6ES in with some Redex and and basically thrashing it to burn the carbon away from ports and chambers. I've just given it a run and it didn't miss a beat but it was only 10-15 miles in traffic and too soon to tell and not worth pulling the plug for a look yet..



I am a little disappointed with the iridium but I did get 600-700 miles out of it. However it must be said I have had a problem sealing the pipe to the head which has only now, finally slotted into place properly and sealed up; I have copper ring number two in there since several ceramic biscuits disintegrated and it may only now have decided to anneal itself and squish into place. And that would have thrown my mix all over the place.



The clue is in the title, "spark plugs always fouling". It fouls, you clean it and it fouls again. Assuming the injector hasn't taken a swan dive or the air filter is blocked. Check for air leaks inlet and exhaust. Check for oil burning (usually obvious). Fit a new plug because the old one may be passé, it's not cleaning up and once they start tracking they don't stop doing it. And clean up the engine, that's important, imo it's not necessary to take the head off to decoke soft soot in the first instance, but it does mean taking it for a long fast run to get the engine hot enough to do the job.

[Dennis C]

Hi Presto, thanks for your agreement but you aren't the someone

[PeteF]

700 miles on a plug! Good grief, I'd be more than a little disappointed. I've had the same one in for 20,000 miles.

[jefrs]

PeteF - that 20,000 is more like what I expected, after all the car's plugs stay in for what, 4 years and can rack up 60,000 or more without attention. But do note I discovered I had a leak betwixt pipe and head. The iridium did clean up but I was not happy with the result. Life is too short to muck about with a £10 plug. I do remember having to bake plugs in an oven to dry them out...

[Caboose]

Hi All

I my youth, every worthwhile roadside garage had a spark plug cleaner available, actually a sandblaster and blow out by compressed air!
Also in the sixties, the motorcycle press carried adverts for a plug cleaner for your toolkit, a necessity if you rode a two stroke, mine in 1961 was a 1958 James Cadet 150cc !
It was a metal cylinder containing many fine steel rods, you screwed the plug onto the end, shook it violently from side to side and the rods penetrated inside and on the electrode to clean it! Very simple and effective.
I wonder if such a tool is available today.

REgards Dick.