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The YS 80and YS 61 ST2 ( they used the same carb on both motors)carb had 3 seperate fuel outlets in the barrel with 3 seperate channels feeding each outlet in the barrel,all the other YS 3 needle carbs have 3 seperate channels in the barrel that dumps into 1 outlet instead of 3 like the 80.Each of the 3 needles has its own fuel suppy passage from the regulator,with a channel that uncovers the passage for each needle as the barel rotates. The idle passage stops functioning after 1/4 throttle,the mid needle function from 1/4 to wide open throttle so it has an effect on wide open and midrange.The high end needle only function from 3/4 to wide open and has no effect on midrange mixture.
On the OS carbs all three needles overlap and have effect on each other,ie: idle effects mid range,mid range and high end overlap at 3/4 opening. If you understand how the YS needles work it is a much easier set up to tune than the OS because idle needle only effects idle and midrange only effects midrange, the idle and high end needles have no effect on midrage setting. So what you do is set the idle needle for a good idle and leave it alone,then set the midrange needle for a good rich midrange,then tune the highend needle for wide open.
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