My freshly restored  DT400 runs fine, but I noticed zero play in the clutchlever, even sliding clutch, when pushing the throttle.  In idle, lever play is as it should be.  As more throttle,  as lower the play up to sliding. Could it be the clutch shaft has too much play in axis-direction? Has it to be adjusted by shims?
Any other possibility?
Your ideas are very much appreciated 
 

No chance, I guess, that the throttle cable is routed such that it pulls on the clutch cable when operated?

Ok what’s happening is for some reason the bearing retainer plate on the main shaft in the case behind the clutch has got dished outwards rather than flat. So— when ya accelerating the helical angled primary gears forces the shaft to the left which takes up your cable play & makes the clutch slip. Close the throttle & it all goes the other way do you get you cable play back again. Sorry to be full of bad news tonight.

Reading your first post again you’re quit correct in saying main shaft has too much axis play. But not a shimming problem. Other thought is if the clutch & its spacer in the middle & various washers aren’t correct so you end up with the clutch hub sitting with free movement even with the shaft nut tight then— look there first before I have you going deeper unnecessarily. 

I see retainer plate 14 is a lot stronger than what i was thinkin g like on my early 250 DT1 360 RT1, so in hindsite i can't see that being the cause. On my older model my retainer plate bending or bowing slightly & letting the bearing & shaft move slightly right & left was probably helped by having very heavy clutch springs so had to push harder to lift the clutch therefor pushing hard on the retainer plate. Just my latest theory.
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Is the clutch axle main support bearing the correct type and does it have the outer locating circlip fitted?

Thank you very much for your ideas.
The engine never has been split, so bearings, washers.. should be ok , inside.
I will remove the clutch and have a look, if washers #13 and #15 are in place. Maybe pulling and pressing on the clutch axle will show play.
Will see next weekend

Wessi, any ideas on my headlight bulb thread?! 

Thanks.