I was pulling 11-12 and my headlights worked.
low vacuum
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Sure!!! Everything that uses vacuum to operate it COULD be hiding the problem. But, that's not how you diagnose a vacuum problem.
First, you disconnect ALL vacuum hoses from the intake manifold and the carb [and cap them off]. Now hook up the vacuum gauge to one of the intake manifold fittings. Start the engine and read your engine's BASELINE vacuum amount. You may have to adjust timing by rotating the distributor to determine the absolute maximum vacuum the engine will make at idle.
If that reading is 13 in Hg, then that's all the engine can make...given the components in it and the age of them (ring, valve wear, etc).
But, I'm betting that you will get something in the range of 17-19" Hg on the gauge. Thus, the engine has plenty of vacuum POTENTIAL...but there are leaks/losses in the vacuum systems -- somewhere.
To find them, hook up one vacuum line at a time and see what vacuum level you get, then. If it drops, there is some cause for leakage in that line/system. Continue to chase it down by blocking off stuff or adding it back in to see when vacuum drops.
That's the general process. Hop to it!!!
First, you disconnect ALL vacuum hoses from the intake manifold and the carb [and cap them off]. Now hook up the vacuum gauge to one of the intake manifold fittings. Start the engine and read your engine's BASELINE vacuum amount. You may have to adjust timing by rotating the distributor to determine the absolute maximum vacuum the engine will make at idle.
If that reading is 13 in Hg, then that's all the engine can make...given the components in it and the age of them (ring, valve wear, etc).
But, I'm betting that you will get something in the range of 17-19" Hg on the gauge. Thus, the engine has plenty of vacuum POTENTIAL...but there are leaks/losses in the vacuum systems -- somewhere.
To find them, hook up one vacuum line at a time and see what vacuum level you get, then. If it drops, there is some cause for leakage in that line/system. Continue to chase it down by blocking off stuff or adding it back in to see when vacuum drops.
That's the general process. Hop to it!!!
Last edited by 7T1vette; Jun 27, 2017 at 11:39 PM.
Pro
Joined: Jun 2016
Posts: 567
Likes: 82
From: Auckland
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
With 15" of vacuum everything including your headlights should work normally. As 7T1vette said, something there is probably hiding the problem. Figure out how much vacuum your engine makes without everything connected and then check each system individually.
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
Curious: Is your engine stock? Heads? Cam? Intake?
My heavily modified engine runs about 7 inches at 900 RPM. Lots of overlap. I have absolutely zero vacuum lines connected to it, not even a vacuum advance or PCV.
My heavily modified engine runs about 7 inches at 900 RPM. Lots of overlap. I have absolutely zero vacuum lines connected to it, not even a vacuum advance or PCV.
Last edited by keithinspace; Jun 28, 2017 at 01:50 PM. Reason: What good is there to ever say about a cat?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski