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1920 Buick


rjp
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Posted (edited)
1 hour ago, Buick35 said:

I think 30 psi

 

Not 30 psi.   

 

If you are talking between the carb and the head, maybe 20+- inches of vacuum on a good motor.  Less if worn.

 

If you are talking "above the carb" meaning before the carb, then zero other than atmospheric pressure depending on elevation.

Edited by Larry Schramm (see edit history)
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This would be about 2" above the carb in the vac. port on the manifold. I have about 10 ft. pounds.  Of coarse I think it should run.

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I doubt that you have 10 foot pounds, more likely you have 10 inches of mercury or 10 inches of vacuum.  Vacuum is read in inches of mercury not psi.  When the engine is running it should develop around 18 inches  possible somewhat less depending on how worn it is. 

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I think a great reading would be about 17" mercury vacuum.  you can play with the spark lever to get the max reading. But a nice steady reading is what you want, Not necessarily a number.

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You can't have a vacuum of 30 psi! Atmospheric pressure is 15 psi so a perfect vacuum like you find in outer space on Star Trek would be -15 psi which is the same as 29.92 inches below atmospheric and it's impossible to get lower than that.

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9 hours ago, michealbernal said:

I doubt that you have 10 foot pounds, more likely you have 10 inches of mercury or 10 inches of vacuum.  Vacuum is read in inches of mercury not psi.  When the engine is running it should develop around 18 inches  possible somewhat less depending on how worn it is. 

 

 AND how wide the throttle is opened.

 

  Ben

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3 hours ago, rjp said:

This would be not running just turning over with the starter

 

Vacuum will be all over the place with the starter depending on which cylinder is drawing and what phase of the stroke that particular cylinder is in. Better to check compression than vacuum. The starter is too slow to measure manifold vacuum. Vacuum is when all the cylinders are firing and you get an average of all the cylinders

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On 7/7/2021 at 11:39 PM, rjp said:

This would be not running just turning over with the starter

 

Take a picture of the tool that you are using for measurement.  Everyone except you believe it is reading in inches of vacuum if you are reading the tool right.

 

Also, from my experience I doubt you would have more than 5-10 inches of vacuum cranking the engine with the starter.  Just IMO.

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