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SUCCESS?????? Sort of! 120-130

posted by  Phil S. on  Mon Dec 4 12:48 CST 2006
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last visit: Fri Oct 24 13:18 CST 2014
[RELATED]

I generally use 20W motor oil (20W-50 is fine).

When the throttle is opened quickly, airflow "gets ahead" of fuel flow and the mixture goes briefly lean, causing hesitation. That's why most carbs have some sort of accelerator pump that squirts extra fuel into the air while the throttle is opening.

SUs don't have such pumps. Instead, the damping effect of the oil slows the rate at which the piston can rise. This forces the air to flow through a reduced opening and air velocity increases. The increased velocity draws more fuel from the jet -- this outweighs the needle being held down in the jet momentarily.

The heavier the oil is, the greater the enrichment. It has no affect on the height to which the piston and needle finally do rise, only on the rate of rise.






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