Thread: vacuum & timing
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Early_S_Man
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It sounds like you have a lot more going on that concern over uneven vacuum! A few basic background questions ...

What was the idle speed before you pulled off the vacuum hoses? Where was the timing with the vacuum hose connected to the vacuum retard diaphram? Do you have the owner's manual or factory 'Spec. book' for your car?

The timing is checked on a '72-'73 MFI engine at two points:

1. 900 rpm with the vacuum hose connected to the distributor, which should be 5 degrees After TDC

2. 6000 rpm (VERY BRIEFLY) with the vacuum hose pulled off the distributor, not to exceed 38 degrees Before TDC

Centrifugal Advance Checks with vacuum hose disconnected:

1000 rpm -- should be 5 degrees Before TDC, note that the vacuum retard is 10 degrees, if your vacuum is acceptable, and the retard diaphram is working correctly! The acceptable range is 3.5-6.5 degrees.

At 1500 rpm - acceptable range 4.5-14 degrees

At 2000 rpm - acceptable range 16-24 degrees

At 4000 rpm - acceptable range 24-31 degrees

At 6000 rpm - acceptable range 31-38 degrees

Have you checked the flow (balance) through the individual injection stacks with a Uni-Syn or Synchrometer?

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Warren Hall
1973 911S Targa
Old 07-03-2000, 08:11 PM
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