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Old 12-28-2007, 01:38 AM   #79
Loose Pre Unit
motu's Avatar
Joined: Dec 2001
Location: New Zealand
Oddometer: 4,598
It acts like the secondary butterflies on a progressive car carb...DCD Weber for example.The diaphram operated secondary comes in at about 1/4 throttle.So the small primary carb works at slow speed,keeping air speed high for good fuel atomization.With a big carb,like 40mm or so on a big single,when the throttle is slammed open air speed practically stops,and the bike they need an accelerator pump to richen them up.Keeping the intake air speed up at low revs makes for a nice smooth running engine.The Yamaha set up works well,but the carbs are hard to extract to do any work on them.I reckon there is a lot of ham fisted attempts at carb repairs on these bikes by people who don't know how they work.....then they blame the set up.
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