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Heads Together Systems - Steve Farmer wrote: > I belive that originally there were larger venturi available for the > solexes. Stock is 23.5mm. I belive the venturi effect creates turbulence > which helps vaporise the fuel better. I think the only other alternative > is "Baby Dells" which can be fitted without major surgery. > Steve, The Venturi is more important than creating turbulance, it works as follows, As the air enters the carb it makes it way down the body, as the diameter gets smaller through the venturi, the air speed increases, this increase in air speed causes a decrease in the preasure (same as aeroplane wings) this decrease in presure is relative to ambient, and thus there is a slight vacum in the venturi. This vacum then sucks fuel from the float bowel through the jet in to the air stream, and on in to the engine. If you make the venturi bigger then the air speed increases less, ther is less vacum and thus less fuel sucked in. This is why you have bigger jets. When the venturi gets so big, the carb body does not taper at all, then I gues you no longer have a carb. Running 34mm venturi in a 40mm carb is much better than a 34mm venturi in a 36mm carb. (Tuning the smaller carb across the whole rev range is also harder). Nic Webb 71 Fastback Team Roobarb & Custard