Adjusting the cut-out of a Lucas regulator isn’t difficult as long as you’re prepared to accept the risk of having to replace the dynamo and/or regulator so if you do any of the below it’s at your own risk.
Be certain of what you are doing and what you must do if the cut-out remains closed and the engine stops. Do not attempt to adjust the voltage regulator as this is very difficult to get correct.
This diagram may help identify the parts.
Regulater/Cutout Box Layout & Settings
Having previously striped the bike for access to the regulator, removed the cover, correctly identified the cut-out points and slackened the adjuster lock nut.
1/ with the engine running at just over tick-over unscrew the cut out adjuster slowly until the cut-out points close.
2/ drop the revs to tick over observing the cut-out points.
2A/ if the cut-out points break then raise the revs again to check that they close, if they do tighten the lock nut, job done, if they stay open raise the revs a little more, if they close, job done if not go to step one and start again.
2B/ if the cut-out contact points are still closed raise the revs again and turn the cut-out adjuster in by a small amount, repeat step 2A.
IMPORTANT:
If at any time the engine stops, and you can start it again within a second or two, do so or you must cut the flow of electricity as soon as possible by one of the following open the cut-out points by hand (careful not to damage them), disconnect the battery or the dynamo. Failure to do this quick enough will burn all or part of the charging system out.
Please note that the bike will not be charging at tick-over if it’s set like this, so if you run the bike at tick-over with the lights on it will slowly run the battery flat.