Thank you for help, I'm really pleased!

I've examined my engine the last days - it's rainig all day - and took some pictures for further discussion... The main deal is, I think the engine was messed up and I have no experinced user nearby to aks how it should look like...

I think someone tried to change the Throttle Arm Set, but stoped halfway... You can see the actual status a the pictures.

I think at Picture 1 the screw C is wrong, I need a 'F5186 Low Speed Needle Valve' to fit in the hole D.
At Picture 2 you can see the screw A. This one looks like an awful replacement. No surprise I could not tune the idle with this.

I think I could fix it up with the throttle arm at the 'original' side... but is there any chance to change the side in a correct way?

@lennyk:
what is the gas port piston mod ? where can i find some instructions?