You will find this forum to be extremely resourceful and full of knowledge, at least I have.
Certainly a good friend indeed to give you such a nice bike!
Have you tried slackening the cable while the bike is running att idle to see if the noise goes away?
The valve lifter was finally set up correctly after much trial and error. Among other things I moved the lever along the handlebar to get the maximum lift on the peg, so it's now on the bend in the bar where the lever moves through a much larger angle. It looks a bit odd but it works. I may have been stupid when trying the various adjustments, as I only looked for the movement of the exhaust valve but didn't try to turn the engine over with the kickstart. It could be that the very slight movement which I didn't see would actually have unseated the valve enough to release the compression, but I only thought of that afterwards! Anyway it now works as it should and with luck I'll never have to touch it again.
Annoyingly getting the clearance on the lifter right had no effect on the tinny rattle at a fast tickover. It occurs at very specific rpm and comes and goes in a regular pattern. It's like a vibration from a loose component or a thin steel panel, but it definitely comes from the engine. You can make it come and go with the advance/retard lever or the throttle twist grip. Several more people have diagnosed it as the little end, but my brother who had the head off reckoned there was quite a bit of slop in the piston, so it's a winter job to find out whether a rebore is needed.
Meanwhile the bike starts easily, cruises at 50 or so and is happier at about 45 mph. It has now done several longer runs and I'm enjoying a very different biking experience. I just need to sort out the front brake which grabs and may need the drum skimming but that's another story.....
