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911 Turbo (930) Forum 1975-1989

Ignition Timing - procedures to set

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Old 06-22-2007 | 05:38 PM
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RodR
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Default Ignition Timing - procedures to set

I'm digging into the 930 tomorrow to check the ignition timing. It seems very sluggish off the line - I think something is goofy w/ the advance (possibly a vacuum leak?)

I believe my car, a 1988 930, has two vacuum ports on the distributor. From what I understand, the correct procedure is to set for stock is:

10 degrees ATDC at 1000 RPM with the two vacuum lines connected

26 degrees BTDC at 4000 RPM with the two vacuum lines disconnected and plugged.

Please let me know if this is correct. Also what function do the two hoses perform (really want to know why there are TWO hoses - ie what the difference is)

Thanks

-Rod
'88 930 Cab
Old 06-24-2007 | 07:52 AM
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Looks correct for a US 930 to me, but my shop manual doesn't cover the '88, so double-check/don't take my word for it.

One line is for the vacuum advance, the other is for the boost retard. It claws back 9.5-11 degrees of advance under boost to prevent detonation. I believe there's also a centrifugal advance, which sometimes gets a little cooked and needs to be lubed and/or freed off.

Hope this helps.

Andy



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