Excess fuel blowing out Dellorto 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

[Storkfoot]

Is it an original carb that, sometime in its life, has spent years out of action? Sometimes, even ultrasonic cleaning won’t clean the internal passages properly.

Is the engine running well?

You are correct that a piston port engine will produce a petrol mist and it will produce a drip or two out of the drain tube.

Have you checked that the float is working correctly? Take the float bowl off. Rest your right index finger under the float and gently push the float up. Switch on the petrol with your left hand. See if the float valve shuts off the petrol.

Have you got the correct float needle? I have come across different lengths and profiles of the V point at the end.

[Trevor S]

Thanks for that Storkfoot.
Its an original carb. Yes, its been out of use (since 1979). I did have a go with an ultra sonic cleaner.
during re commissioning and made sure there is no leak on the manifold. I replaced the slide. All the
jets appear standard.

What other clues? The piston rings are new - could it be some blow back?

I think the engine is running well, but as yet I have not driven it on the road.
I will check the float and that the valve works. I replaced the valve with a new one but did not look closely.

The SX is all ready to go otherwise.
Trevor S

[hullygully]

Probs just needs a blat down the road bud