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FJR Motorcycle Forums
Technical & Mechanical Problems
How do you precisely measure engine vacuum?
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<blockquote data-quote="ELP_JC" data-source="post: 281513" data-attributes="member: 6177"><p>Never needed to actually measure engine vacuum before... until now, so want to do it right (over the weekend).</p><p></p><p>Engine pulses (vacuum, no vacuum...) cause a gauge or a 'stick' to bounce, as we all know. If we want to measure 250mmHg, like in our case, there are 2 possibilities:</p><p></p><p>1. Gauge or stick only goes to HIGHEST vacuum, meaning the highest bouncing level is the accurate vacuum reading.</p><p></p><p>2. Gauge or stick goes BEYOND true vacuum due to momentarily sucking then abruptly stopping the vacuum, causing the gauge/mercury/etc to shoot past actual level, meaning the middle of the bouncing is the correct reading. Having said that, I'd imagine with a spring-loaded gauge, or heavy mercury, there's less of a chance of this happening, than say, with ATF or something lighter. Comments welcome.</p><p></p><p>So what is it? Let's start the debate.</p><p></p><p>PS. I'll use a Craftsman vacuum gauge to measure 250mmHg on #3, then mercury sticks to balance rest against #3.</p><p></p><p>JC</p></blockquote><p></p>
[QUOTE="ELP_JC, post: 281513, member: 6177"] Never needed to actually measure engine vacuum before... until now, so want to do it right (over the weekend). Engine pulses (vacuum, no vacuum...) cause a gauge or a 'stick' to bounce, as we all know. If we want to measure 250mmHg, like in our case, there are 2 possibilities: 1. Gauge or stick only goes to HIGHEST vacuum, meaning the highest bouncing level is the accurate vacuum reading. 2. Gauge or stick goes BEYOND true vacuum due to momentarily sucking then abruptly stopping the vacuum, causing the gauge/mercury/etc to shoot past actual level, meaning the middle of the bouncing is the correct reading. Having said that, I'd imagine with a spring-loaded gauge, or heavy mercury, there's less of a chance of this happening, than say, with ATF or something lighter. Comments welcome. So what is it? Let's start the debate. PS. I'll use a Craftsman vacuum gauge to measure 250mmHg on #3, then mercury sticks to balance rest against #3. JC [/QUOTE]
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FJR Motorcycle Forums
Technical & Mechanical Problems
How do you precisely measure engine vacuum?
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