Hello, new here and hopefully I’ve put this in the right section.

A few months ago I bought a lovely 1969 CT1 off of Peter who’s a member on here.

I’ve only recently started to take it out to break the engine in, which highlighted an issue as I stayed out riding when it got dark.

As soon as I switch the key into position II for lights, the bike will either cut out unless I hold the idle high with the throttle, but even then it’s loosing spark as you hear it misfiring badly. Under load it’s pretty much half power and will just cut out as soon as it drops below 2000rpm. The lights will come on then turn off also whilst riding and the rear light is super dim.

Things I’ve done so far:

- Replaced the lighting coil for a NOS Yamaha item and replaced the condenser.
- Checked the ignition switch as I thought this may be going to ground on position II, all checks out fine.
- Cleaned up the battery ground and charged the battery.

I’m kind of out of ideas on what it could be, I can’t see anymore grounding points on the bike. So any help is very appreciated as I’d love some lights!

Thanks
 

Welcome to the forum. I’ll be following this thread with interest because my CT1C does the exact same thing.

I have a 69 CT1. I resto'd the bike and decided to put a new NOS, NEW N O S Switch on.

RESULT:
if you as much as jiggled the key it would disconnect charge.

REASON I FOUND:
It was not making good contact between the two connecting surfaces.

THE FIX:
The back plate on the switch was not pinched down tight enough. The tighter you pinch it, the
harder the key is to turn and the better the switch works. You have to find a happy median.
As soon as the key started to turn smoothly I left it there and
it seems to work.

Not sure if this helps but may be worth looking at. If the key is real loose to turn, thats a sign of a loose back plate.  Maybe consider disassembling and inspecting
the switch.   Even a new NOS switch is 60 years old.