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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Apr 2010 Posts: 283 Shop Shark | | Shop Shark Joined: Apr 2010 Posts: 283 | Also before we declare "abnormal vacuum" let us consider altitude at your region or maybe you have a test or testemony from a carbureted engine in your area.
Modern engines at idle might see 21 or 22 inches @ sea level changing to 17 inches @ 5000 ft altitude.
Bob Taylor
| | | | | Joined: Oct 2006 Posts: 163 Shop Shark | | Shop Shark Joined: Oct 2006 Posts: 163 | So I adjusted my valves and figured out why I was showing 13" of vacuum yesterday when I had been showing 17" just a few days ago. When I reinstalled the carb yesterday after removing the jet I forgot to plug my vacuum advance port on the carb. I plugged it and now am showing 17" I'm at 2k ft so I read you lose about 1" for each 1K ft so that would put me around 19" at sea level.
Took the truck for a ride aorund the block, runs great.
I've closed my book on this problem. | | | | | Joined: Apr 2010 Posts: 283 Shop Shark | | Shop Shark Joined: Apr 2010 Posts: 283 | Jason we're happy for you and I know the rest of your family must be glad the problem is resolved too.
Thanks for the good feedback, and we'll give an A for thoughtful diagnosis and determination.
Bob Taylor
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