LOW vacuum

'87 Chevy G20 Van
At Idle, I have about 19-20 inches of vacuum...running down the road at 50-60 there is about 9! as soon as a mild hill is encountered, 3 inches of
vacuum! It pulls the hill with little loss of speed.
Why is the vacuum so low going down the road?
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The vacuum drops as the throttle plates are opened....this is normal behaviour. Pick a cruise speed where you have maximum vacuum and this where you will get the best mileage.
--
Mad-Dog
'79 Chevy K-10
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I know this! That IS the best the vacuum gets! It should be MUCH higher!

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Get a backpressure test done. Probably the CAT is plugged up big time.
"Shades" <shades_1970(at)netins(dot)net> wrote in message

at
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No cat. Was removed by a previous owner.

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"Shades" <shades_1970(at)netins(dot)net> wrote in message

My uncle used to time his truck by the vacuum gage. Don't remember exactly how he did it, but I do remember the drastic difference a few degrees would make.
Maybe the timing has slipped or the chain has jumped a notch.
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RJ in WV

What do you do if the biggest hammer doesn't work?
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That would affect idle vacuum to though. I am installing a new timing set this week along with a water pump. Both have 140K on em. I will see if that does anything.

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