The slant on the shaft can be very worn. The steel ball at the end of the horizontal push rod grooves a hole into the slant, what makes adjusting the clutch very hard. I would losen the excenter srew and pull out the shaft to see, if its ok.

Okay, I misunderstood the instructions. I'll check that today!
I have noticed that the lever moves up and down. So I will use the screws on the Bowden cable to bring the lever back to the position behind the main bolt and then try to take out the play with the eccentric screw. Then screw in approx. 1/8 turn, according to the instructions.
One more question: The service manual states that a dimension of 5.5 mm should be checked. Does this mean the distance between the engine and the center of the clutch lever, which can be moved up and down by the eccentric screw? Is this then adjusted using the adjustment screws on the Bowden cable?
Wessi, The eccentric screw should be able to be unscrewed completely when the lock nut is loosened? I couldn't unscrew it completely.
RT325: Unfortunately, despite deepl translation, I didn't quite understand what you meant :/

I had to look back to see what lies i told haha.
I was assuming the clutch was trying to drive with the lever pulled back to the bar, but think i miss-understood the problem.
I meant if the 'clutch center' the plates fit onto has been off & re-fitted with any spacing washers trapped then the center might not revolve so if you put it in gear it would just jump forward.
Anyway, sorry, i don't think that was the problem you were having so ignore my post.

512_Newbie, you've made some assumptions and/or misunderstandings of what the instructions say.  Which are not hard to misunderstand, the instructions are not very clear.  A little later I will attempt to clarify the process...  for example, best practice is to back off the bowden cable adjustment at the handlebar lever completely as the instructions say.  You will probably never get it right if you try to set the lever with the cable before adjusting the eccentric.  I actually prefer to remove the cable completely sometimes.

More later, I have a few things to do before it gets too hot here.

Hey Mark, I just had some time to try out what you described.
The adjusters on the Bowden cable are set so that there is a lot of clearance. Then adjusted the lever all the way down with the eccentric screw. Then set the clearance on the handlebars using the adjusters on the Bowden cable.
Maybe that wasn't right either, because it doesn't change anything. You have to push the bike slightly forwards or backwards to disengage the clutch. Once it disengages, it doesn't close again until quite late!
As an experiment, I also tried setting the lever at the bottom of the motor all the way down and then the adjusters on the Bowden cable very far out. As I understand it, the clutch should now disconnect permanently or the lever should not reach the handlebars at all.  But that didn't change anything either. But perhaps I should have waited for your detailed answer ;-)

I've forgotten what bike, but you say the arm is under the motor I think, so down is for the arm is maximum adjustment & if on top of the motor then up is max. Anyway, if you do that then adjust the cable & nothing works then I'd guess you'll need to go in to the clutch & see what's going on, or not going on!!. Could the ball be missing, if it is meant to have one there. If it's the fat rod with large shaped ends then no ball required.

I did a test drive when I bought it and everything worked fine. Then it was picked up by a haulage company and delivered to me. Since then there have been these problems.
The ball can't suddenly be missing or the push rod bent.
I looked at the clutch disks first.
I hope that it is a fault in the clutch adjustment after all.
Otherwise, I'll get on with the next tasks. If I can't get any further with the clutch, I'll remove the lever and check it. If that doesn't help either, I'll have a second look at the disks. I have Monday off, so I'll get on with it

If you remove the clutch cover again you can see the clutch lift & separate if you pull the clutch lever back to the bar. You could pop it into gear & push it forward & back while in gear if it's separating properly. There's no way to check if its going to slip or grip when under power though until the cover is on & rideable.

Clutch
Make sure you're using wet clutch oil and it sounds just gummed maybe.... up if you can rock it and break it free?

I dismantled the clutch disks a second time. There were still some deposits on the steel plates.
After reassembly it was a little better, but the symptom was still there.
I made it roadworthy again and took it for a test ride. Lo and behold, the clutch is now working well again!

To push the bike I still have to shift into neutral or push the bike back and forth, to disengage the clutch. But that doesn't bother me, now I can get on with the other tasks :-) Maybe driving will make it go away.

I use Motul 10W30 mineral transmission oil. As I remember, there was no further manufacturer information from Yamaha