Sparking points

[Wack]

I've not messed with points for 30 odd years but my LI Special has a problem starting but once running will tick over quite happily once warm but whilst cold it misses a spark every now and then and usually cuts out. When it is running I noticed the points sparking and occasionally the spark jumps to the points base plate, this is when it misses. I changed the points to GP double sprung ones but didn't change the condenser when I rebuilt the motor, could it be the problem?

[Captain Pugwash]

Could be condensed it usually shows arcing at the points when they fail.

[Wack]

Changed the condenser for another original(all I had) this afternoon and plastic type HT coil and although the points don't spark as much, only faintly now and again, the scoot still suddenly cuts out. There's a cracking spark at the plug so seems strange why it just stops. Obviously tried other plugs and caps, new lead and disconnected the ignition switch. Tried a 20mm carb but it and the 18mm both have 45 pilots and I'm now wondering if this could be the problem as they both run the same unless I keep blipping the throttle. I've an electronic kit I could try but was trying to keep the scoot as original as possible but may try it just to rule out anything electrical then if it still does it I'll know it's carb related.

[grandpa]

Hi Wack,
Is the engine earthed? You get weird faults with poor earthing might explain why spark is tracking down to points base plate.
Grandpa

[Wack]

Yes , still using the original braided wire and checked with a meter. I have wondered about the LT coil but have no figures to work to.

[coaster]

Have you got a NEW condensor to try? They do lead quite a hard life so not impossible that both of yours are faulty. Also wort checking that the insulations are clean and assembled properly.

[Wack]

Tried starting again today , it would fire up then cut out so fitted a fine wire plug and hey presto ticked over lovely . Took it for a ride, stopped for 1/2 hour and it struck up straight away. So even though the fat tipped plugs had a brilliant spark maybe they needed a bit more voltage to fire under compression compared to the fine wire plug. Fingers crossed

[Captain Pugwash]

Is it a resistor plug ?

[Wack]

It is at the moment with a non resistor cap until I can get another plug. Kicked it over tonight and started first time again.