1968, ? on vacuum lines 4 distributor - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 12-14-2011, 07:36 PM Thread Starter
 
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1968, ? on vacuum lines 4 distributor

I'm working on friend's 1968, 350 2 barrel Lemans. The vacuum lines for the vac advance were not installed correctly upon arrival. There is no ported vacuum source but 3 manifold sources. Did Pontiac use straight manifold vacuum for the dist? There is also what appears to be a temp activated vacuum switch screwed into intake manifold water jacket. I'm quessing the vacuum advance does not go into effect until after it's warned up. Does this sound about right? Thanks
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post #2 of 4 (permalink) Old 12-14-2011, 10:46 PM
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Originally Posted by supercab78 View Post
I'm working on friend's 1968, 350 2 barrel Lemans. The vacuum lines for the vac advance were not installed correctly upon arrival. There is no ported vacuum source but 3 manifold sources. Did Pontiac use straight manifold vacuum for the dist? There is also what appears to be a temp activated vacuum switch screwed into intake manifold water jacket. I'm quessing the vacuum advance does not go into effect until after it's warned up. Does this sound about right? Thanks
Yep. I'd have to dig around for the diagrams and connections but you're right. That switch on the water crossover part of the intake was used to control the amount of vacuum advance (and in some cases vacuum retard) based on engine temp. It was part of the early emissions systems. My 69 had one of those too, but I decided it was a dandy place to install the temp sensor switch that controls my electric cooling fans.

Also to be sure about what those ports are, test them with the engine running. I've got two vacuum sources on my QJet that are so low that I would have sworn they had to be non-ported sources, but feeling them with the tip of my finger while blipping the throttle told me otherwise.

Whether to use a ported or a non-ported source for vacuum advance tends to be one of those "great debate" topics that people fight about. Try 'em both and use whichever one your engine tells you it likes.

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post #3 of 4 (permalink) Old 12-16-2011, 03:53 PM Thread Starter
 
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Ok, thanks; that should be enough info to get us by.
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post #4 of 4 (permalink) Old 12-16-2011, 06:44 PM
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Bear is correct, IMO. Originally, these cars all used manifold vacuum, not ported. I run both of mine on manifold vac, as they seem to run better (cooler, better mpg).
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Projects, Barn Finds & Restoration Discussions

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