Dual or Single Vac advance ?
- Thread starter Bort62
- Start date
A
Anonymous
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I've got a dual and have had no issues. There used to be a great explaination of the diferences and advantages posted on this forum. Do a search, its worth reading.
I don't think the search works back that far anymore. Everything prior to the 11/1/03 crash is there, but not searchable.
The dual hookup vac advance has a second vacuum hookup that actually retards the spark. I forget actually what mechanism was employed to produce this "retarding vacuum" but nevermind. It was for emissions purposes, to be employed when too much advance would result in poorer burns.
The middle hookup in the classic location works the same as always in these dizzies. You can use them with the second vacuum port left open, as they do not NORMALLY communicate. However, note my emphasis there. If the diaphram in the advance were to fail, I suppose you could get a vacuum leak, with dirt getting into your engine. Just a theoretical idea of mine, but it would be a real pain if it occured. (Maybe this could occur with other dizzies too???)
Now, make sure you are not confusing dual vacuum hooks with a dual advance dizzy. A "dual advance" dizzy is one that has both vacuum and mechanical spark advance. This is a very real consideration, especially for older small sixes that came with loadomatic dizzies. These units relied on vacuum advance only, but it was a modified vacuum from special carbs that have a "spark advance valve" (Holly 1940, Autolite 1100 and 1101 for instance).
If anyone want more about loadomatic, say the word, and I'll try to relay all that I know. I got most of my knowlege right here, but most of that stuff is older and thus unsearchable.
later...
The dual hookup vac advance has a second vacuum hookup that actually retards the spark. I forget actually what mechanism was employed to produce this "retarding vacuum" but nevermind. It was for emissions purposes, to be employed when too much advance would result in poorer burns.
The middle hookup in the classic location works the same as always in these dizzies. You can use them with the second vacuum port left open, as they do not NORMALLY communicate. However, note my emphasis there. If the diaphram in the advance were to fail, I suppose you could get a vacuum leak, with dirt getting into your engine. Just a theoretical idea of mine, but it would be a real pain if it occured. (Maybe this could occur with other dizzies too???)
Now, make sure you are not confusing dual vacuum hooks with a dual advance dizzy. A "dual advance" dizzy is one that has both vacuum and mechanical spark advance. This is a very real consideration, especially for older small sixes that came with loadomatic dizzies. These units relied on vacuum advance only, but it was a modified vacuum from special carbs that have a "spark advance valve" (Holly 1940, Autolite 1100 and 1101 for instance).
If anyone want more about loadomatic, say the word, and I'll try to relay all that I know. I got most of my knowlege right here, but most of that stuff is older and thus unsearchable.
later...
