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931 S1 vacuum advance/retard..

 
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2002
Location: MI

PostPosted: Mon Jul 20, 2020 6:45 am    Post subject: 931 S1 vacuum advance/retard.. Reply with quote

The boost retard line is the one on the backside of the can right? Goes to the brake booster hose/manifold vacuum..
The one on the front goes to the ported vacuum on the TB right?

If so, then why does my idle change if I remove the line on the back of the can and plug it, while my idle does not change if I remove the line to the front of the can and plug it?

Confused..

I figured removing the boost retard line on the backside wouldn't change anything except for on boost, but this doesn't seem to be the case..
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kondzi  



Joined: 02 Jul 2018
Posts: 95
Location: MZ/Poland/EU

PostPosted: Tue Aug 11, 2020 7:19 am    Post subject: Reply with quote

Not sure about 931/S1, but Iíve recently had a strong headache from 1986 930 US. This has two vacuum cans - one for boost retard, the other for vacuum advance control with additional idle advance when cold. The trick was there was US emissions system that advanced idle ignition a bit at cold engine by blocking vacuum to the idle can (letting in atmospheric air instead) When the engine warmed up, the solenoid valve opened and a fully functional vacuum advance was operational.
Maybe, but just maybe itís similar in 931/S1?
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2002
Location: MI

PostPosted: Thu Aug 13, 2020 3:17 am    Post subject: Reply with quote

Mine doesnít have any valves in the middle of the vacuum lines..

I was just trying to figure out a way to stop it from regarding so retardedly much on boost, quick and dirty style..
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