Has to do with the orientation of the carb opening - Saab Sonett Bulletin Board - Saabnet.com
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Has to do with the orientation of the carb opening
Posted by Jeff Bartlett [Email] (more from Jeff Bartlett) on Mon, 13 Aug 2007 21:20:26
In Reply to: Progressive carb and MSS manifold, Sean, Mon, 13 Aug 2007 18:22:20
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on the manifold. If I understand it correctly, on an MSS manifold, the opening is oriented along the long axis of the manifold.
A progressive 2 barrel carb has one throat open at partial throttle, with the second throat, usually of a larger diameter, opening only when much more throttle is used. Half throttle is usually only half throttle on the smaller throat. The second throat may not open until you get to what you think would be 75 or 80% throttle. I think these throats are what Chaz is meaning when he wrote of jets, which I think of as a much smaller part of a carb which controls how much fuel is allowed into the throat.
Anyway, if a progressive carb is pared with a MSS manifold, at part throttle the throat that is open is physically much closer to two intake runners than the other two, leading to two cylinders running richer, while the other two will be leaner. At full throttle, when the other larger throat is opening, the lean/rich relationship will be reversed.
With a sequential carb, both throats are the same size, and open equally, so at half throttle, both throats will be open the same amount. With a sequential carb, both "pairs" of cylinders - front pair and rear pair - should see very similar quantities and ratios of fuel and air, and the cylinders will experience much more even loading.
No guarantees that this is accuate, and I've been very wrong before, but this sort of make sense to me.
posted by 70.17.9...
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