Engine cuts out when lights switched on, but...

[EddieStone]

It only does it after a while.

Background: I've restored my 1963 Li150, kept everything original including 6V electronics. It's a battery model. I've owned the scoot since 1990, and it's been off the road since 2001. So now it's back on the road, MoT'd and I'm slowly finishing off the restoration.

Problem is the engine won't run when the main/dipped lights are turned on, but it only does it after about 10 minutes or so. It was fine for it's MoT. It always starts second or third kick from cold and first kick when hot and runs happily when the lights are off or on sidelights.

I'm thinking it could need the flywheel remagnetizing, but I've had this in the past and it was difficult to start rather than cutting out when the lights were turned on. It could be the stator? What would I look for? I'm also wondering if I've wired it up incorrectly, but I can't see how it would run at all if I'd done that.

Any suggestions welcome. I appreciate I should fit an electronic 12V kit and I'm planning to. But this will involve changing the crank, flywheel and top end. I just want to ride it around for the moment until the paintwork is sorted. This set up got me all over the UK in the past with no problems so I can't see why it's not playing ball now!

Any help welcome.

[Daggs]

First step; remove the spark plug and close the gap up. Yes i know it sounds ridiculous, but mysteriously it works (sometimes) on original 6V systems.
Though it probably indicates a need to remagnitize.

[HxPaul]

You dont need to change the crank or the top end to fit an electronic ignition.

[EddieStone]

You dont need to change the crank or the top end to fit an electronic ignition.

Yeah, I know, it's just that I'm planning a conversion which will require a GP crank and TV top end. I'd like to get it running OK as standard while I save up for the kit!

I'll try adjusting the spark plug gap tomorrow. Thanks for the tip.

[bristolmod]

points gap as well.

[Tractorman]

points gap as well.

I remember this problem in my youth with the points system. As Bristolmod say check the points for setting or just dirty.

[EddieStone]

I've just adjusted the plug and I think it's cured it! Thanks guys!

The gap was about 0.7mm, so I've adjusted it to 0.4mm and it started second kick (on the stand!) and sat there ticking over quite happily with the lights on full beam. I'll check the points and give it a road check tomorrow as I've got a gig to play this eve.

Thanks again you've saved me hours of headache!

[FREAK]

plug gap is too big

[EddieStone]

Thought I'd update this thread. The plug gap was indeed too big. I closed it up and went for a ride last night and it was fine. Lights had no effect at all. What a bizarre fault.

Thanks again.

[Chris in Margate]

You're too young to know better, not like us old farts !