Hitchcocks Forum

Has anybody got tips on the best spark plug ?
I have a highly tuned Bullet export 1995 535 cc , 9:1 comp ratio .
I seem to churn through NGK B9ES far too much and they soot up pretty fast , are hard to clean as I dont have my electric grit blaster plug cleaner any more ( nobody seems to have stocked them for many years } .
, Champion spark plugs seem to go up in smaller increments and far more swirl area with a longer center pin making them easy to clean , right now I'm on a Champion N5,is good for starting and it spits back less ...just past slow tick over . Due to the incredible warm sunny days since summer it's 20 degrees every day here in Sydney so I put off changing my Amal slide to a number 2 for our so called winter .
Does anybody else find NGK's have a short life ? The single cylinder engine with a missfire is hell so I carry spares but Champions seem to last longer overall . Does having a resister in the plug cap weaken the spark power . Does having a twin plug set up improve combustion ?
I changed my Lucas coil to a BMC Austin Mini coil which is oil cooled and though still made by Lucas it's just a little fatter in size , could this be part of my problem ?

A lot of the old car coils were designed to run on a less than 12v. The voltage being reduced by a ballast resistor which was bypassed only when the starter was operated, to give full voltage to aid starting. If this coil is the same and you are feeding 12v continuously to it then it is liable to over heat and break down. The standard plug for the 500 is a B8ES, a B9ES is a colder plug and will be more liable to foul up, as the plug will not get hot enough to burn off the deposits. It may be worth trying a B8ES. NGK plugs number a different way round from the rest, the higher the number the colder the plug. A champion N5 is hotter than the standard N3 and will therefore burn off the deposits better hence why you get on better with them. Hopefully I have got that the right way round!

Hi - there are lots of things going on there!

Just commenting the plug - if your NGK fouls-up easily then either it's too hard (and stays too cool) or you're running too rich.
The Champion N5 has a heat range of around the same as an NGK B6 - which suggests that in your bike the NGK B9 is far too hard and will never gets hot enough to self-clean.
(The longer nose on the Champion may show it's a softer plug - the longer nose exposes more of the ceramic plug tip to the heat of the combustion chamber and dissapates heat more slowly, letting the plug run hotter, so the tip gets to a temperature high enough - between 400 - 800 degrees c - to burn off carbon and self-clean.)
My choice is always for NGK - but getting the right heat range helps.
Best regards

Even in an untuned 500cc EFI the NGK B9ES fouls pretty quickly. Watsonian didn't recommend them.

Hey , thanks for the plug info .
I feel a bit stupid to have forgoten that Champion numbers are the reverse of NGK , my N5 Champion was too hot by 2 numbers and risks blowing a hole in the piston if the engine was loaded going up hills .
My NGK heat rating of a B9ES was too cold , I'll get some B8ES plugs and everything should be good running on 98 octaine fuel .
Sydneys winter rains have now started...

Try an Iridium plug, it will cost you about $20 but will last 20000kms at least. They are NOT to be cleaned at all. The reason sand blasters are not used these days is they round-off the the tip of the centre probe; the spark is stronger when the edge is sharp and square, the same applies to contact breaker points, better to use a file or stone than emery cloth on them.

Phil your state of tune is not particularly high therefore as Leon suggests fitting an NGK BR8EIX Iridium plug may well go part way to resolving your problem. .... then sort out the carburation if indeed the plug is still sooting up. .. however there have been occasions where it is oil that is doing the fouling especcially when the wrong grade plug is being used as appears to be so with you as you say you're using BR9 ES. .. But on the other hand there are many folks who consider iridium plugs to be no more than snake oil.

I have a skimmed head with 40 thou reduction with a forged piston and a 2mm reduction plate at the base of the barrel plus a thin head gasket , I think 8:1 comp ratio , it a hard engine on 98 octaine so I can go up and down in ratios , I have the right plug now I hope

I'm really pleased with the effect of the right grade plug , it's transformed the engine which is now very smooth in the low rev range and has a much more solid slow tick over where it used to splutter and die . All this bleeding time ( 10 years ) I had the wrong grade plug , the engine feels more powerfull but I have no proof , a very good starter when hot . For years I thought if you raise the comp ratio you use a cooler plug , I found this out as a teen when I blew a hole through a piston .
It seems Bullets are far more flexible in the control of combustion temps , , It great when something dramaticly changes from something that bugged me that things were not right to what now seems perfect and for only $5

Hi Phil

Forgive my stupidity here, but removing 40 thou from the head is equivalent to 1mm then to fit a 2mm compression plate to the bottom of the barrel is putting the 40 thou back plus another 40 thou which will lower the compression not increase it, or have totally misunderstood what you are saying?.