rjp Posted July 5, 2021 Share Posted July 5, 2021 What is a good vacuum reading on on a 1920 Buick 6cyl. At the manifold above the carb? Thanks Link to comment Share on other sites More sharing options...
Buick35 Posted July 6, 2021 Share Posted July 6, 2021 I think 30 psi 1 Link to comment Share on other sites More sharing options...
Larry Schramm Posted July 6, 2021 Share Posted July 6, 2021 (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 July 6, 2021 by Larry Schramm (see edit history) 2 1 Link to comment Share on other sites More sharing options...
rjp Posted July 6, 2021 Author Share Posted July 6, 2021 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. Link to comment Share on other sites More sharing options...
michealbernal Posted July 6, 2021 Share Posted July 6, 2021 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. 1 Link to comment Share on other sites More sharing options...
Oldtech Posted July 6, 2021 Share Posted July 6, 2021 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. 2 Link to comment Share on other sites More sharing options...
Morgan Wright Posted July 6, 2021 Share Posted July 6, 2021 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. 1 Link to comment Share on other sites More sharing options...
Bloo Posted July 6, 2021 Share Posted July 6, 2021 My head hurts. 1 2 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted July 6, 2021 Share Posted July 6, 2021 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 2 Link to comment Share on other sites More sharing options...
rjp Posted July 8, 2021 Author Share Posted July 8, 2021 This would be not running just turning over with the starter Link to comment Share on other sites More sharing options...
Morgan Wright Posted July 8, 2021 Share Posted July 8, 2021 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 1 Link to comment Share on other sites More sharing options...
Larry Schramm Posted July 11, 2021 Share Posted July 11, 2021 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. 1 Link to comment Share on other sites More sharing options...
EmTee Posted July 12, 2021 Share Posted July 12, 2021 1 2 Link to comment Share on other sites More sharing options...
Morgan Wright Posted July 12, 2021 Share Posted July 12, 2021 56 minutes ago, EmTee said: Vacuum salesman comes to the door, whip out the manifold vacuum tester, say "Does electrolux pull 24 inches of mercury like the one the Kirby guy had?" 1 1 Link to comment Share on other sites More sharing options...
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