une R 80 R qui ratatouille à partir d'une certaine vitesse

you are welcome... here you are at your house.

Bon soir,
I finally found some Information about my trouble in a German forum:

http://forum.2-ventiler.de/vbboard/showthread.php?66577-unerklärliches-Problem-im-quot-höheren-quot-Geschwindigkeitsbereich/page2

One idea is about the carburetor membranes having become too soft.
The second idea is about the level of the float in the chamber of the carburetor. This is quite difficult to check because of the uneven surfaces.

I guess I will try new membranes as a next step to solve the Problem.

A bientot

Lothar:
for checking the level of the float in the chamber of the carburetor:
Takes a plastic bottle; Cut the bottom; Removes the carburator tank
Instead, places the bottom of the bottle and open the tank tap
 like this , you'll see the level of the float
Good luck

Bon soir
hello again,

it seems that I finally found the cause of the problem: The slides of the carburetor were rough on the surface and needed polishing. Anyway, now after polishing the surface of the carburetor slides the engine runs perfect.

I received help from Brune in Telgte/Germany. Manfred Brune built the famous K 1 Turbo and carburetor version with the Martin frames in the late 1980s/early 1990s.

au revoir
Kind regards

Lothar