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Post Info TOPIC: Vaccum pressure low at the carb, remedies?


Veteran Member

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Posts: 62
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Vaccum pressure low at the carb, remedies?


hi Again,

1963 Laurentian with 1966 Chev 250 inline 6.

In preparation for my trip, I am trying to do my own tune up. I changed plugs, new air filter. I put a vacuum pressure gauge on the carb.  With the engine warmed up, it draws about 7-8 on the gauge. We used a dwell meter and set the idle to 1000, 1050 rpms. That pulled the reading up to almost 10. From internet research, that is still low. I have a cracked distributor cap (electronic ignition). Not sure if that is affecting timing or not. Low reading suggestion from online: blowby due to worn piston rings, possibly late ignition or valve timing. An extremely low reading could also indicate an air leak at the intake manifold. I haven't done a compression test.

Any suggestions or thoughts on this matter or what I might be able to do? Thanks as always!

 

Roy



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Poncho Master!

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Make sure that you check the vacuum at the intake manifold. Depending on the carburetor you may not be reading true manifold vacuum if you are hooked to a port on the carburetor. If the car has an automatic transmission you could disconnect the vacuum line for the transmission modulator valve and use the port on the manifold for your gauge. If its a manual transmission try and use the pcv valve hose for your test. Manifold vacuum should be about 20 when idling.

Paul

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Veteran Member

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Posts: 62
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Great information! I was on the carb port. I'll do it again. and send an update!

Thank you!

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