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79-930
 
Join Date: Apr 2010
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1979 930 distributor vacuum line connections

I understand the vacuum and pressure line connections to the throttle body but not sure which pod on the distributor is for retard or advance. I see a large pod on the distributor, right above the hold down nut, when standing behind the car. Another vacuum line goes between the distributor and engine block connecting to the distributor. Does anybody know which line is retard, which line is advance?
Old 08-04-2017, 07:24 PM
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The dizzy rotates in CCW direction looking down at the top. The port on the can pointing towards the back of the car is vac retard, it moves the advance plate in a CCW direction retarding the timing at high vac conditions. The port on the front of the can is boost retard, it moves the plate in a CCW direction under boost pressure to pull timing back from full centrifugal advance.
Old 08-05-2017, 06:09 AM
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79-930
 
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Quote:
Originally Posted by boosted79 View Post
The dizzy rotates in CCW direction looking down at the top. The port on the can pointing towards the back of the car is vac retard, it moves the advance plate in a CCW direction retarding the timing at high vac conditions. The port on the front of the can is boost retard, it moves the plate in a CCW direction under boost pressure to pull timing back from full centrifugal advance.
Thanks
Old 08-05-2017, 01:57 PM
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I'm not sure that this is technically correct. Doesn't the vacuum line give vacuum advance at low rpm, then go to 0* advance once vacuum goes to zero.

Rahl
Old 08-06-2017, 07:51 PM
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It's a matter of semantics. The vacuum pot retards timing under vac, boost pot retards timing with boost pressure. Retard decreases as vac. decreases. When there is no vac and no boost the centrifugal advance mechanism and the static timing you set determines the timing.Here's the centrifugal advance and vac/boost retard curves for the two pot USA dizzy.

Old 08-07-2017, 01:09 PM
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