Jeffko says...
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Direct manifold vacuum will add timing to your initial timing at the damper at idle and nobody with any idea about what they were talking about would suggest that.
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Guess you missed at least ONE reason why using intake vacuum could be BETTER than ported vacuum. It's a way to address engine 'run on'. And yes, I know exactly what I'm talking about!
Jeffko says...
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Using ported vacuum your vacuum advance will react more quickly and fall off with the loss of vacuum at wot which is where the mechanical advance will have taken over.
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Not in MY opinion, and the 'theory' can be easily proved with a vacuum gauge and a timing light. As soon as the throttle plates OPEN the carb port there is no measurable difference between ported and intake vacuum, they are the same, originating from the same source. As ported vacuum falls off, so will intake vacuum at the same rate until the carb port closes. Intake vacuum will respond FASTER than carb ported vacuum because it doesn't have to 'wait' for the port to open. 8" or 20" of vacuum is vacuum, regardless of the 'source' (port or intake).
No offense to Jeffko, just a differing of opinions on a complex subject.
