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[Davie Hall]

Hi all I took my electra X out the other day and while it normally starts 2nd kick, I had somehow put the kil switch in the off possible so after about 4 kicks.it started smelling of fuel. I put the kill switch back to run and it started next kick. Once it had reached normal operating temperature it was misfiring on a constant throttle but ran ok under load. Once I got home after approximately 20 miles I removed the plug to find it black and sooty.I cleaned.the plug and tried it again and it still misfiŕes. This is the third it has had in 3k miles
I ran it without the plug cap on by holding the ht lead against the plug and.it has a good strong blue spark that will jump a 15mm gap without breaking down so that to me suggestions the coil etc are all good and the plug cap is new.
Does anyone know how to stop it eating plugs or have I just been unlucky?

[Exile]

A 15mm gap...?? Jeeeeezus! That's over a half inch...


My Thumper did this too.. and then I shifted to electronic timing and the problem disappeared.. (Not that I'm an expert or even rate myself as a mechanic..)

[PeteF]

If the plug was black and sooty the engine is probably running rich. You haven't left the choke on have you? It has been known.

[Davie Hall]

No Pete I didn't leave the choke on, been caught out by that one before. I have recently replaced the throttle cable but that's all. I have had the jets etc out and they are all clean. I thought with a good quick run the plug would have cleaned up

[Adrian]

There have been some comments about the current NGK's not being very resilient to sooting up. What make of plug are you using, as a matter of interest?

[Adrian]

Sorry, and what grade of plug? A.

[Gwilly]

Have you still got a catch can which overflows into the air filter. Worth checking the filter and the can.

Working with the theory of what did you touch last.. Did you disturb the carb when fitting new cable? could the float level have altered? got crap on the needle seat..

Diaphragm still ok? if its a CV type.. Failing that try an iridium plug..

[Presto]

Now to ride a hobby horse:

We hear too many reports of plugs ‘failing’, iridium and standard type spark plugs. Sometimes the ‘failure’ is put down to modern petrol. But that’s very unlikely: those who use the same fuel in bikes and cars don’t have their spark plugs fail. It’s also very unlikely that the problem is down to faulty plugs or plugs of poor quality (although there are reports of non-genuine plugs in circulation.)

Seems to me that the most common cause of ‘plug failure’ is fitting a plug of the wrong heat-range.

Quotation from NGK official literature:
‘Carbon fouling is the most common spark plug related failure, but is not a spark plug fault. Carbon deposits are conductive, and as they accumulate along the insulator nose they reduce the insulation resistance of the spark plug. As electricity always takes the path of least resistance a misfire may occur if a significant amount of carbon deposits accumulate. A spark will not form as electricity can track along the conductive carbon deposits to the metal shell (as shown in red below) rather than forming a spark across the electrode gap which has a very high resistance.’

‘The optimal operating temperature range for a spark plug is 450 – 870°C, 450°C is the spark plug self cleaning temperature at which point carbon deposits will burn off. However, if too cold (hard) a spark plug is used and this temperature is not achieved carbon fouling will occur. This is the most common reason for carbon fouling.’

‘As carbon builds up, the insulation resistance of the spark plug drops and the voltage generated by the ignition coil is reduced. When the generated voltage becomes lower than the required voltage of a spark plug (the voltage needed to cause sparks at the spark gap), sparking is suppressed and mis-firing occurs.

‘Wet fouling is fundamentally similar to carbon fouling. The insulation resistance is reduced allowing a spark to track along the insulator nose and earth to the metal shell rather than forming a spark across the electrode gap as desired.’

Fouling of this type occurs when

a] fuel mixture is too rich – incorrect carburettor setting and/or blocked air filter
b] electrical current is too weak, poor connections or faulty ignition
c] engine run for an excessive time on tickover
d] continuous low speed running – the plug fails to reach self-cleaning temperature
e] incorrect heat range of plug – too cold (hard): the plug does not reach self-cleaning temperature; too hot (soft): the plug over-heats, causing detonation, engine seizure, and rapid ware to the electrodes.

[Adrian]

That's a very worthwhile consideration, especially if, like me, you tend to err on the side of too cold a plug (to be on the safe side!) I think the recommended (non-Iridium) NGK plug for the Electra-X (with a resistor plug cap) is the B9ES, which certainly IS a hard/cold plug, with plugs of that range specified in view of the Electra-X being a hot running lean-burn engine, at least as far as the factory intended. But how many of us still using these bikes have kept the lean-burn carb/PAV/restricted exhaust pipe intact? And do we always have a long enough ride to get the engine good and hot? Maybe try a (genuine) B8ES or even a B7ES or the Champion equivalent if your lean-burn engine isn't so lean burn any more, but keep a close eye on the state of the plug for signs of overheating. A.

[Thack]

Just for the record, I'm currently running a BP5ES in my bog-standard 2014 Bullet 500.