spark plug issues

lee emmett · L Plate Warrior Joined: 22 Sep 2012 Karma :

I have a 2007 Royal Enfield electric start 500cc I use it for occaional use only .But recently I have been Blowing spark plugs like fuses.The bike stops i clean up the plug it still shows a spark but not a strong one but does not start,i replace it with a new plug and the bike starts first time.I use the reccomended plug BR8ES NGK type.the charging system ok as is the battery.Ireplaced the coil as I thought it may be this, even tried Iridum plug but no joy.So if i ride out now I have to always carry a spare plug with me to get home.
Anybody got ideas it is the plug as i have put a resistance meter on the plug and it shows some resistance compared to a new one.

regards

yen_powell · World Chat Champion Joined: 22 Jun 2008 Karma :

What colour are the electrodes when you take the non working one out? Sooty black by any chance?
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Nick 50 · World Chat Champion Joined: 24 Jul 2011 Karma :

Lee,

It would be better starting a topic in the Workshop part of the forum, (or if a mod could move it?) as the Forum Feedback & Help part is more to do with help needed using the site not bike help.
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raak · Spanner Monkey Joined: 21 Dec 2006 Karma :

yen_powell · World Chat Champion Joined: 22 Jun 2008 Karma :

YBR Ric · Spanner Monkey Joined: 16 Jan 2012 Karma :

Once a (near invisible) conductive coating has built up on the insulation around the centre electrode allowing the spark to short back to earth it renders the plug virtually useless for its originally intended application.

lee emmett · L Plate Warrior Joined: 22 Sep 2012 Karma :

yep spark plug is sooty but clean it up and does not work and this plug shows some resistance via meter.

have tried mixer screw on carb have set it to manufactures guide,never had the plug its a single cycinder by the way,a tan colour.

I have heard ideas float in carb too high but why should this change??
it has a pankcake type air filter i am think of changing this to a bellmouth kind whether the air filter is resricting the air flow?

have heard changing the plug to a champion type but their must be an issues to make the plug blow?

it just gets to a point its not worth riding as i always have to change the plug or ride very local in case i have to push home.

raak · Spanner Monkey Joined: 21 Dec 2006 Karma :

temeluchus · World Chat Champion Joined: 01 Oct 2008 Karma :

Is it electronic ignition or points?

Have you checked the coil?
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YBR Ric · Spanner Monkey Joined: 16 Jan 2012 Karma :

Have you visually checked the air filter ? Emulsified oil expelled from the crankcase breather can saturate the filtration medium resulting in a very rich mixture and plug fouling.

Your bike should have a Mikcarb Vm28 fitted, float height 24-26mm.

Fitting a bellmouth on your Mikuni copy, will reduce the venturi effect over the emulsification tube. A larger jet holder will probably be required as well as a bigger main jet, different fuel height, a change of needle position and possibly a different throttle slide as well to compensate for the intake pressure drop.

Fitting a replacement K&N filter might be a better option.

bikersupermot... · Could Be A Chat Bot Joined: 26 Jul 2008 Karma :

hi lee

any progress with your spark plug issues?

iv got a gilera gsm50 supermoto that gets used couple times a year and i got exactly same issues going on with that - it also uses br8es plugs and after about 70 miles - the bike cuts out and wont restart - put in a new plug and off it goes again!. and then after about 70 miles stops again, new plug and away she goes etc etc

why do these bikes need a pplug with a resistor in them that burns out?
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lee emmett · L Plate Warrior Joined: 22 Sep 2012 Karma :

The resistor in the plug stops /suppresses electrical interferance with the bikes electrical moduels if you have them.
Haven't had time to work on the bike this weekend but set next weekend to deal with.
Re coil replaced this but still has the problems so if it gone again possaible issues then further back.

will keep you all post on my developments.

lee emmett · L Plate Warrior Joined: 22 Sep 2012 Karma :

YBR Ric · Spanner Monkey Joined: 16 Jan 2012 Karma :

What leads you to believe you have resistor problems - is a nearby am/fm radio suffering interference whenever the engine is running?

It's unlikely for consecutive plug resistors to fail (unless they all came out of the same multi-pack from the same dealership) but a slight possibly the plug cap resistor may have failed.

Most likely (if you have one) its a metal covered plug cap which leaking HT to earth. This can easily be checked in the dark for tiny bluey white sparks where it clips onto the plug body hexagon.

If it's anything electrical at all for the symptoms you have described (hows the air filter by the way? ) it's likely to be the advance and retard bob weights have worn through the back of the capacitor - which can only be seen by unscrewing it and checking.

Budgetboy · Scooby Slapper Joined: 05 Apr 2012 Karma :

Try a hotter plug NGK BR7ES as that might help.

carbon fouling is caused by air/fuel mix wrong,bad compression or ignition problems. Thumbs Up

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lee emmett · L Plate Warrior Joined: 22 Sep 2012 Karma :

Matt- · World Chat Champion Joined: 19 Jul 2012 Karma :

Ignition to retarded or too advanced.

Basically not getting a optimum burn.

Matt
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YBR Ric · Spanner Monkey Joined: 16 Jan 2012 Karma :

The 'book' figure (1/32" fully retarded) which equates to 32* at full advance is what was originally quoted when these bikes first left Redditch. A time when motor vehicles ran on much lower octane fuel. It's been faithfully quoted ever since. Using modern petrol with its far higher octane rating to what was available over 50years ago means if set at 32* on full advance that the ignition runs too retarded.

The other thing with a Classic iron barrel Enfield is you don't need 5k ohms of plug resistance in addition to 5K ohms of plugcap resistance.
If you use a decent NGK suppressed plug cap to protect say an electronic ignition upgrade then you can happily use a B8ES OR a B7ES if you're going for a different grade to burn the carbon off, although ideally you want to stop it getting there in the first place, not get rid of it afterwards. Too rich a mixture could lead to petrol wash, ring damage and then oil seepage up into the combustion chamber and a oiled plug.
Reducing HT ignition resistance should improve your plug spark.

What is causing the sooty plug?
blocked filter (too little air)
choke on (too much fuel)
other carb problem
revertion to a quieter more restrictive exhaust system.
Counterfeit NGK plug which is an incorrect grade for the bike?