# Vacuum advance hose routing 4 speed



## mbergin (Jun 19, 2012)

Hi all. Should be an easy question. I have a 69 GTO with a 428 4 speed. The car came from the factory with no thermo vacuum switch (not installed for manual transmission cars) so I removed the broken tvs installed by the previous owner and plugged the manifold with a NOS plug. I replaced the carburetor with the correct 69 manual transmission rochester quad. The only vacuum ports I have now are in the manifold or above the throttle plates in the carb. When I plug in the vacuum advance to the carb or the manifold, the idle increases and the timing advances making me think that I need a ported vacuum, which I can't seem to locate. 

Can anyone with a 4 speed 69 goat tell me where their vacuum advance line is connected?

Thanks


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## geeteeohguy (Feb 2, 2008)

Manifold vacuum is the factory spec, not ported. Manifold vacuum will help it run cooler at idle and low speed, and gives better drivability on these cars. Set the base timing (about 6 degrees BTDC with the hose disconnected, then re-connect after the base timing is set and adjust the idle speed and mixture and you'll be good to go.


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## lars (Sep 28, 2004)

:agree
That's correct. For a detailed description of this, and the specs and operating principles, drop me an e-mail request for the "Vacuum Advance Control Units & Specs" paper.

Lars
[email protected]


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## mbergin (Jun 19, 2012)

Thanks geeteeohguy and Lars. You obviously have a lot of knowledge on this subject and i appreciate the guidance.

My apologies....I failed to mention that the engine has an HEI ignition and a mild cam. When I originally timed it I played with a few different settings (didn't seem to want to run below 9 btc but I may have had the idle too low) and was satisfied with 12 btc (vacuum advance disconnected) as this setting did not cause pre-ignition or detonation. The book calls for 9 btc for the 1969 428. With this in mind should I still go with 6 btc? 



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## geeteeohguy (Feb 2, 2008)

No. More initial advance is a good thing if you can get away with it without pinging, etc. Do contact Lars, as he can give you a very thorough and comprehensive education on all things tune-related.


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## pontiac (Mar 6, 2011)

the HEI vacuum advance will be all wrong for this setup.


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## lars (Sep 28, 2004)

pontiac said:


> the HEI vacuum advance will be all wrong for this setup.


Not neccessarily: That all depends on which vacuum advance control unit happens to be installed on the distributor - there are appropriate ones, and inappropriate ones, just as there are with the standard points-type distributor vacuum advances. My Vacuum Advance Specs paper has the specs for all the vacuum advance units, including HEI and points-type. Select an appropriate unit, and it will run great.

mbergin: You also need to get away from the concept of setting the initial timing to some single-digit spec... set the timing up for total timing (should be in the 36-38 range as a starting point) and tune per my timing paper for best performance.

Lars
[email protected]


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## mbergin (Jun 19, 2012)

Thanks Lars. I timed the engine today (total timing at 36 degrees at 2800 rpm). Having some pinging so I will retard 2 degrees at a time until the pinging is alleviated. Still need to work with the vacuum advance. Ill let you know how I make out Thanks so much for your help. 


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