Sticky butterfly valves

[rerb]

Hi, The throttle on my b12 doesn't return when let off, I thought it was a cable/tension issue but after replacing them I noticed that the throttle linkage on the carbs barely returns when disconnected from the cables. I cleaned everything up with carb cleaner and sprayed some wd40 on the outside linkage but it's still stiff. Is there a way to internally lube the valves without getting lube all throughout the carbs? thanks. 

[Joseph]

Petrol dabbed on using a new paintbrush ?

[MeanBean49]

Just use wd40 throughout, wont be a problem 

[cnap504]

WD-40 good for metal, not good for rubber, especially slide diaphragms 

[Swiss Toni]

I’d take them off, and ultra-sonic them. Just done the neighbours        ...night & day!