Thread: No Vacuum

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I have a 1948 chevy truck with a 350 from a 1972 chevelle in it. It has been sitting for 20 years but I got it running, however I can not get it to idle low enough without dying and it is only making about 6 in of hg of vacuum. Any ideas what could be causing this? I have tried to find a vacuum leak using the carb cleaner method but have not had any success.

Read this first: Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

After sitting for 20 years I'd say the carb is clogged with varnish and most if not all of the hoses are shot.

I rebuilt the carb and have replaced the hoses so I'm pretty sure it will be a leak around the intake manifold

Did you do a compression test?

PCV valve? Valves adjusted or perhaps hung up?!?!

Repeat: a step-by-step evaluation process is here: Check Your Engine’s Health: With a Vacuum Gauge | Tuner University

If you want to keep guessing without a good process, you're going to waste a lot of time.

Thanks!! I read the article and I believe it is either a vacuum leak or a problem with the cam timing. I did do a compression check and it was ok.

1972 is about the year Chevy had a batch of bad cams. Possibly yours has wiped the lobes.

To diagnose if there are cam lobe issues pull the valve covers and use a dial indicator to check the lift at each of the push rods. If you don't have a dial indicator you can buy one, and a magnetic base, at Harbor Freight for about $20.00.

And here's another [http://www.secondchancegarage.com/public/186.cfm]How to Use and Interpret a Vacuum Gauge[/url] link that shows various gauge scenario's:


Hope that helps,

John