timing
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From: Centreville USA
I assume you have a vacuum advance? If so, did you set the timing with the vacuum advance disconnected and plugged at the carb? Are you using timed vacuum (from above the butterflies) or manifold vacuum? Are you sure your timing marks are correct. Your engine could just like 15 degrees BTDC. Mine is happiest at 10.
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From: Centreville USA
Originally Posted by edsf100
does it matter if you switch your vacuum line to the non-emission plug on the carb? I noticed the idel changes. 390 stock cam.
Fleet Mechanic
Joined: Sep 2004
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From: Rowland Heights
I couldn't check for vacuum on my old Holley since I couldn't get it started. I hooked up the vacuum advance to the non-emission port on the edelbrock and noticed a difference in performance but I have hard starting after the engine sits awhile. The fuel lines and running over the intake and the electric pump is set at 7psi and the psi should be at or below 6.5psi.
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Fleet Mechanic
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From: Rowland Heights
Thanks, that was the location of my line. What is the lower port near the manifold on the holley for?
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Post Fiend
Joined: Mar 2004
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From: Union, Washington
It's for running vacuum driven goodies, like some switches that control the EGR and the temp switch that makes the timing advance when the engine gets too warm so the thing idles fast enough not to die. Vacuum advance at the dist. should have zero vacuum at idle, which is what the ported vacuum port gives you. Manifold vacuum is highest at idle which would advance your timing when you don't want it to be. Vacuum advance is to give you better mpg when your engine is under a light load.
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From: Centreville USA
Originally Posted by ford390gashog
i hooked the vac advance to the metering block on the holley
Senior User
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From: Centreville USA
Originally Posted by edsf100
Thanks, that was the location of my line. What is the lower port near the manifold on the holley for?
Senior User
Joined: Jan 2002
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From: Centreville USA
Originally Posted by Bear 45/70
It's for running vacuum driven goodies, like some switches that control the EGR and the temp switch that makes the timing advance when the engine gets too warm so the thing idles fast enough not to die. Vacuum advance at the dist. should have zero vacuum at idle, which is what the ported vacuum port gives you. Manifold vacuum is highest at idle which would advance your timing when you don't want it to be. Vacuum advance is to give you better mpg when your engine is under a light load.
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Joined: Jan 2002
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From: Centreville USA
Originally Posted by edsf100
Thanks for the info. This helps. I have a C6 and the vacuum was hooked up to the lower port on the Holley 4779, 750, is this correct?
Fleet Mechanic
Joined: Sep 2004
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From: Rowland Heights
Thanks "bluesky636". Any info on adjusting the PSI on a Comp Pump by Mallory. It's a series 110 model 4110. It pumps 7psi and my carb "edelbrock says no more than 6.5psi. The pump states on the web that there is limited adjustment but I can not find any info on "HOW TO". Do I need to worry about a difference of .5 psi?