TS has misfire when lights are on. Help

[TS Tom]

Hi . New to this forum and need help.
I have a 1975 TS 125 and after getting it out of the garage after the winter it now has a misfire when the lights are on and the engine is hot, fine when cold and the lights on.
It runs great when they are off hot or cold.
Any help much appreciated.

[jabcb]

What kind of ignition system does your bike have? (magneto, PEI, alternator & points)

Are you indicating that:
1) you can ride for a while with the lights off & everything is fine, then
2) turn light lights on & it runs badly, then
3) turn the lights off & everything is fine

Is the battery fully charged?
Are the lights working correctly, with both hot & cold engine?

[TS Tom]

What kind of ignition system does your bike have? (magneto, PEI, alternator & points)

Are you indicating that:
1) you can ride for a while with the lights off & everything is fine, then
2) turn light lights on & it runs badly, then
3) turn the lights off & everything is fine

Is the battery fully charged?
Are the lights working correctly, with both hot & cold engine?

It has an alternator and points.

Yes you have it. 1.2.3

The battery is charged

The lights work, if not a bit dull, with a hot and cold engine.

[tz375]

It sounds like the battery isn't being charged. I'd start by cleaning the battery terminals and then check voltage at teh battery, off, turned on and running at idle and at say 5000 rpm.

That will give you a place to start.