carb - air bellow's, what do they actually do?

[hank]

who can give me a technical reason for the air bellow/metal bushing setup on 16, 19 & 20mm carbs? seems a bit elaborate to me

why not just a small rubber tubed section clamped on like you use for bigger carbs?

[Juan]

The metal part is to clamp the carb,the rubber boot is to keep the shit off it.

[ozzy]

rubber bit also keeps your scooter from filling up with shit... which improves mpg

[hank]

still not convinced - if you just used a thick short length of rubber tubing clamped/jubilee clipped onto the manifold and the carb, it would do the same wouldnt it? the 'bellows' shape and the metal bushing shape just seem too much considering the simplicity of the timeless vespa engine anyway, i've included a new bellow, metal bushing, clamp, bushing ring and washer in my recent SIP order, so i'll set it up and report back, or i'll just forget about it and use my 24mm carb instead

[breezer]

I found the rubber bellows wouldn't fit when I put a malossi manifold on, so I just left em off...

dont think they are VITAL

[tony]

bellows was indeed to keep out the rubbish but also to help utilise the frame as an airbox and therefore fairly constant. Air is fed in under the horncast-above the mudguard and flows through the chassis to the area around the carb.
Don't use one on mine though!

[hank]

the metal bushing (32 in diagram) wont fit on my ets manifold, its got a large lip part way down the tube. when i got the engine the manifold was on the engine and the carb was seperate with a carb clamp on it. so it looks like you just push the tube into the carb, clamp it and thats that no bellow, no metal bushing. there is an internal rubber ring just inside the carb mouth so i presume that provides an air tight seal.