Vacuum advance
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Joined: Feb 2007
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From: Buhl Minnesota
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
The carb has 2 types of vacuum sources on it: Ported vacuum and manifold vacuum. It doesn't matter whether you change the vacuum from the carb to the manifold. It matters if you change from ported vacuum to manifold vacuum. Manifold vacuum is available at the carb or at the manifold. Changing from ported vacuum to manifold vacuum (by changing the vacuum hose from one nipple on the carb to the other) will change engine efficiency and fuel consumption at very low throttle openings, but not at cruise speed where ported vacuum and manifold vacuum is the same.
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Joined: May 2006
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From: Dayton, Ohio
I knew you were going to ask that and I cant honestly say.I can tell you several years ago I tried ported verses manifold on my own car and I know the manifold made the car more responsive but I think I got better milage on the ported.If it would have been a bunch I think I would have remembered.My car was driven in town only for that little unprofessional test over about a month.Maybe Lars can say which way is best in theory for milage in town.
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Joined: Feb 2007
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From: Buhl Minnesota
The carb has 2 types of vacuum sources on it: Ported vacuum and manifold vacuum. It doesn't matter whether you change the vacuum from the carb to the manifold. It matters if you change from ported vacuum to manifold vacuum. Manifold vacuum is available at the carb or at the manifold. Changing from ported vacuum to manifold vacuum (by changing the vacuum hose from one nipple on the carb to the other) will change engine efficiency and fuel consumption at very low throttle openings, but not at cruise speed where ported vacuum and manifold vacuum is the same.