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Forum: C3 Engines, Driveline and Handling

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vacuum

Posted: 9/22/07 2:00pmMessage 1 of 3
r
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tallahassee, FL - USA
Joined: 7/20/2007
Posts: 9
Vette(s): 1977 l-48 corvette tan, 87k miles, all original
One of my buddies brought his 82 over the other day to check a trans leak. Well, Two guys and a Corvette, ya gotta play as long as the wife will allow. We were checking his head llight actuators. He had just had them replaced and wondered why they were moving so slow and taking forever to open and close. I started checking the plumbing aginst the ones on my 77. Then I pulled a hose off to set it better and noticed that there wasn't much vacuum. I got out the ol gage and it was readying 6lbs of vacuum. I checked my vette and was getting 18. 18 is on the lower end of the green on the gage. I checked vacuum in different locations some from intake and some from carb base. even under acceleration, it never got over 12.  I haven't checked the compression yet, but low vacuum is a sign of low compression isn't it??  
 
I need to also note that it was born with FI. The guy that was doing his mechanic work pulled the FI off and installed a quadrajet. Could that be a problem with his vacuum?? whadayathink???  T
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vacuum

Posted: 9/22/07 5:44pmMessage 2 of 3
R
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BINGHAMTON, NY - USA
Joined: 7/19/2003
Posts: 3825
Vette(s): ......
Has the cam been changed ? hotter cams can lower vacuum

C3VR Lifetime Member #93

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vacuum

Posted: 9/22/07 6:12pmMessage 3 of 3
s
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baytown, TX - USA
Joined: 4/21/2004
Posts: 160
Vette(s): 1979 maui blue/doe skin, fuel injected 383, 6-speed manual, hooker sidepipes, 3.90 gear

Vacuum readings at idle much lower than normal can indicate leakage through intake manifold gaskets, manifold-to-carburetor gaskets, vacuum brakes or the vacuum modulator. Low readings could also be very late valve timing or worn piston rings.

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