I would add hight tautness of belt

I thought than solex carb hasn't adjust. Could you told me how can I do it? I think that it's ok, but I'm not sure.

Since I put an suitable air filter on my 340 (last own had an very slim filter; and air passed free by top and down), fuel consuption has rised considerable. Is there any kit performance or other car replacement for air filter system for volvo ·$= !:/ with solex?