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 FOR NOS SWITCH INSTALL
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. 

Maybe ask Peter for some background info on what work he carried out, and if he had the same problem.

If I recall correctly, the lighting and ignition circuits aren't linked.

By memory lighting & ignition 'are' linked in that the ignition source earth's into the lighting coils. So if your points are too wide or dirty or your plug gap beyond 20-22 then something magic or 'bad' magic happens when lights activated. Close plug gap & probably be ok. Check points gap although that determines timing but would be good to keep it at 12-24 max. Also if the lighting coils are loose & possibly shorting within, it can cause that too. My guess is close the plug down if fitted as it came out of the packet?. Had all that on my HT1 90 but have seen that problem at work back in the day.

I’ve spoken to Peter, he’s actually having a similar issue on one of his bikes. I don’t think he would of been aware of the issue on this bike as he only rode it down the road.

I’ll check the point gaps, the lighting coil is all tight in there. Everything inside the magneto looks great.

I’ll check the plug and see what it’s gapped to. Such a odd issue, as from my checks so far everything seems to be working as it should.

Gr8uncleal "Maybe ask Peter for some background info on what work he carried out, and if he had the same problem."

Alan, this Peter chap sounds a bit dodgy to me  , the bike Craig has is my '69 CT1 (it was just too pretty for me to ride).
Morley thanks for the tip.
Craig, I cleaned and gapped the plug on my CT1-C today and it runs and rides without any issue with lights on.
 

"Alan, this Peter chap sounds a bit dodgy to me." 

Yes, very - he doesn't seem to be responding to emails at the moment! 

plug gap update?

You could check the grounds on the points, condenser, primary ignition coil, magneto plate, engine to frame and secondary ignition coil to frame. They should all be a fraction of an ohm.

I had a motorcycle from Florida that I did a bunch of work to. New points, condenser, painted the frame, etc. I made sure the engine to frame and coil to frame had good metal to metal contact not through paint. The engine would idle perfectly but as soon as you opened the throttle it would lose power and die. It turned out the condenser to magneto plate resistance was 20 ohms. I cleaned mild corrosion off the magneto plate and got the resistance to a fraction of an ohm. Bike ran perfectly after that!