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dashpots 120-130

posted by  Phil S. on  Thu Mar 1 06:48 CST 2007
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last visit: Fri Oct 24 13:18 CST 2014
[RELATED]

20W or 20W/50 works for me.

There's not a debate about it, really, and no one weight is best. It's just that people misunderstand how SUs work and get it backwards.

When you open the throttle, air rushes into the motor and it takes a moment for the fuel from the jets to catch up, so the mixture goes lean and you get bogging. If the piston is held down by the oil, the air is forced through a smaller opening right over the jet and draws more fuel from it even though the fatter part of the needle is still in the jet. The heavier the oil, the longer the piston rise is delayed and the richer the mixture.

The oil has no effect on how high the piston rises, only on how quickly it does it, so it doesn't impact mixture at steady throttle openings.






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