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I'm not familliar with "470" Holley's. Holley presently makes a 390 and 450 mechanical secondary 4160 style carbs. Are the 470's vacuum secondary units?
Chances are they are equipped with an 8 or 8.5" pover valve. Check your manifold vacuum at idle. The power valves should be 3" (inches of vacuum) lower than the manifold vacuum at idle.
Example. If your car idles at 6-7" of vacuum you should have a 3-4" power valve in each carb or the power valve will open prematurely or even be open at vacuum creating a rich condition at or just off idle.
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michael
A man that is young in years, may be old in hours, if he have lost no time. But that happeneth rarely. Generally, youth is like the first cogitations, not so wise as the second. For there is a youth in thoughts, as well as in ages... Sir Francis Bacon (1561-1626)
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