still not starting

[Andy Kay]

Hi,
Totally unrelated to a C15, but I recently had exactly the same problem with an old Suffolk engine.
Wet plug, big fat blue spark but no go.
Just about to throw the towel in when I swapped the Champion plug for an NGK.
Fired first pull!

[Tigerfeet]

My pal replaced the loom on his Tiger Cub - and put the wires to the three position ignition switch on incorrectly.  C15 has same switch with emergency position...  Just a thought.

[Barnsey]

I think that, if the ignition switch was incorrectly wired, I would have no spark.   That said the resistance of the switch and the ammeter could have an effect.   

Last night, I topped up the charge in the battery and kicked it over.  It coughed once and then no more. So I left the battery on charge over night.  But no joy, no cough nothing. 

SO, new plug, new spark lead, new battery all seem good options.

   This is the sad point where I throw money at it until it starts working.  Always sad to buy new parts only to see it have no effect. 

[Barnsey]

BTW the plug is already a new NKG (B8ES)  . I wonder what the odds are that it might be faulty?  I wish I had the old one., but I swapped them months ago. Any suggestions as to the best plugs to use gratefully received.

[Barnsey]

Okay, I dug around and found the old plug, which happens to be iridium, but it didn't have any effect

[Kernowpete2]

Two heads are better than one. Maybe there's a member in your area who could pop over and help

[rhyatt]

So, before the loom change all fine and running
Now , after loom change , not running.
Obviously retrace every step , does every other function work correctly ? Go over every single function.
If it is only this ignition area that is defective then at least its narrowed to a manageable area
You have the 2 separate  areas of supplying the ignition coil with electricity,
Normal on and EMG
Concentrate on the normal on path 1st and get it running there

[iansoady]

I would try a jury-rigged live direct from the battery to the coil (disconnect the loom wire from the coil). This will make sure you're getting the full voltage there. 4-5 volts is very low especially with a fully charged battery.

[Andy Kay]

With regards to spark plugs. I read recently that there are a lot of counterfeit NGK plugs around, especially on EBay.
The advice is to source plugs from a known a reputable place.

[V500]

Very true, although there is a page on the Net giving the signs to look out for with counterfeit plugs.
Surely the OP has a spare plug (or one from another bike) that he could try in the meantime? As Mr Soady says above, a simple flying lead wired from battery to the coil feed would check the ign switch and associated wiring.

[scifi]

You mentioned sometime last month, that you only had 4 volts on the coil.  This should be over 6.5v if your battery is Ok.   So can you trace all the wiring from the battery to the coil, to see where you are loosing the 2 volts..?    If the battery is only 4v then try starting when you have a battery charger connected.

[Stevegayler]

Isn't an NKG (B8ES) a bit hot. I used to use this in a Velocette Venom with rather a high compression ration. I would have thought a softer B6.....or similar would be a better option.

[Barnsey]

Maybe you are right, but it shouldn't stop the bike starting should it? The bike came with the B8 iridium plug and it was running before. 

[Barnsey]

BTW  the sump was dry too.  We checked that this evening. 

[Dripfedfloor]

I'd thoroughly check the earth connections. I'd also advise that you get someone to check the volts on the coil while it's being kicked (Dad had a Mini with an earth fault; it lost all power to the coil when being cranked). This is reading like an earth fault to me. Low voltage on the coil hints at a resistance somewhere in the system.