Fuel vapour blowing out the carb

[Trevor S]

When I run my 1967 SX200 with the air hose off, there is fuel vapour blowing out the carb mouth when I
rev the engine. I have noticed fuel dripping out of the drain tube with the air hose in place.
The Dellorto carb has been cleaned fitted with all new gaskets, slide, and fuel cut off valve etc.
I have never had a Lambretta that did not leak fuel out the drain tube a little however I think this
is a bit much.
Anyone solved this?
Trevor S

[hullygully]

how old is the bore to piston to rings bud?
does the piston match any tuning work done on the barrel?
timing?
carb & jetting?

[hullygully]

think you need to place this in the carb section bud