Hitchcocks Forum

Hi there,
I am using the NGK BR8EIX Iridium spark plug in my 500 Bullet (carb engine). This spark plug shows a very, very light grey colour in contrast to a light brown to brown colour I know from conventional spark plugs. Saying this, I am unsure whether the very lite grey indicates a lean mixture or Iridium spark plugs generally show other colours and therefore can´t be "read" like conventional ones. Appreciate all info/hints, thanks Peter

I have no experience of iridium plugs in a carb engine but I did try one in my EFI C5. I can't say that the colour itself was any different to an ordinary plug but I would say that the colour charts in Haynes and similar seem to reflect what plugs used to look like when petrol was petrol and not some horrible concoction as it is these days. The plugs in all my bikes seem to look weak on modern fuel and they do seem to have more of a grey than a brown hue on the electrodes, usually with a darker rim round the plug body. In the end I went back to a standard NGK because I found that the thin electrode on the iridium plug was less tolerant of fuelling inaccuracies that afflicted my EFI, which I have sorted now. FWIW I have set the plug gap to 0.5mm as recommended by our host. This has made a definite improvement.

With an injector the insulation colouration is misleading, it tends to be paler. With a carb you should get the typical colour indication of rich or lean - if you shut off immediately after a run and do not let it idle. There again modern fuel burns cleaner and usually has ethanol in it, so the colour charts are probably out of date; expect paler colouration.



The only problem I had with the iridium is the electrode is the size of a pinhead. My bike was fouling the plugs then due to poor sparks, and the iridium with its tiny electrode fouled quickest of all because it could not find a clean spot to spark from.



A bleached appearance (grey?) usually means the plug is too hot (or mix weak enough to cause pinking) but the BP8EIX is a cold plug. So ???

I had a BR8EIX in the Bullet for nearly 20,000 kms. The only advantage with them is they last longer. Recommendations on the box said not to clean and not to adjust the gap; which I didn`t. Fit with a smear of anti-seize and forget. I only changed it because it was too cold for the state of the engine and was starting to soot- up. The are used in modern cars because it is becoming a major job to reach the plugs and they will last for something like (not sure) 80,000kms in a car.

Hi Peter, for a carb type engine, I would use a plug with the least numbers and letters - a B8ES is all you need, even more so if you have points, as you don't want or need a resistor with them [BR prefix]. At the end of the day, if the mixture is being lit satisfactorily and at the right time and by the right grade of plug, I see little point in chasing letters and numbers in the vain hope that your engine will gain power or run smoother, unless your fancy plug has replaced a duff standard one, of course. Regards, Paul.

Many thanks to all - I think I will go for the B8ES (as per Paul´s reply). Peter

They may last longer (but plugs in cars always seem to last longer and give far less trouble than in bike engines). I fit them and always would (Denso for preference) - my experience is that they make starting noticeably easier. I can’t detect any other benefit to performance (speed or fuel economy).

Hi Paul... why "the least numbers and letters" for spark plugs for a Bullet? I have tried the Iridium plugs, but somehow they don't work for me. I haven't figured out why, and since the B8ES works fine, I continue to use them. I use B8ES with a resistor cap and the bike has points, so I also have to ask what you mean by "don't need a resistor with points". Looking forward to learn more about the electrics on my bike... Jacob

Hi Jacob, if you read my post again you will see I mean the fewer numbers and letters on a spark plug the better is what I mean, from my point of view anyway. I have 'fixed' a few bikes in recent years which had misfires and poor starting and running, including a Honda CB500F, which had resistor plugs and resistor caps, which would only run on two cylinders. The owner handed me an electronic ignition kit to fit and fix it with, he was amazed when I handed the kit back after fixing the bike with 'ordinary' spark plugs and told him to send the unused electronic ignition kit back for a refund. With points, you don't need either resistor plugs or plug caps and you certainly don't want both, but I am probably banging my head against the wall trying to get through with this one. Ho hum, each to their own etc. Regards, Paul.

Hi JTL: I think what Paul means, is if you use a resistor plug ie, BR8, with a resistor
cap and there is probably a carbon resistor high-tension lead to the plug there will be too much resistance. Too much resistance means the spark can`t jump the points gap and there is misfiring. Resistors were necessary to block static in car radios and communications two-way radios. In the good old days with copper high tension leads to the plug and no resistors; neighbours would see and hear static on their TVs and radios as the vehicle went past their house. These days, most household appliances have filters to block this out.