This is a simple idea for anyone using a 35mm TMX Mikuni carb on Lambretta.
 
Mikuni carb spigots are shorter than normal Amal carbs.
 
Most mounting rubbers freely available for the Mikunis are the Amal carb type.
 
If you use this mounting rubber as you tighted the jubilee clip, the rubber deforms and is acting on the Mikuni to push it off the mounting rubber.
 
This MB alloy ring fits into the mounting rubber first, then fit the carb - now the jubilee clip cannot deform the rubber s the carb should stay on longer and the rubber should last longer.