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View Poll Results: Vacuum gauge reading in neutral at idle (800 RPM) | |||
Don't know | 5 | 41.67% | |
Less than 10 | 0 | 0% | |
10 to 12 | 0 | 0% | |
12.1 to 14 | 0 | 0% | |
14.1 to 16 | 2 | 16.67% | |
16.1 to 18 | 4 | 33.33% | |
Higher than 18 | 1 | 8.33% | |
Voters: 12. You may not vote on this poll |
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Thread Tools | Display Modes |
#1
IP: 138.207.175.58
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Poll - Vacuum Gauge Readings
Vacuum gauge readings in neutral at idle (800 RPM)
Last edited by Administrator; 12-14-2018 at 01:26 PM. |
#2
IP: 71.208.62.184
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I hook up a vacuum gauge once in a while but have not installed a permanent one yet. It is on my list.
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#3
IP: 73.212.47.219
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On my list, but behind a bunch of other things. If only boating were cheap, I would have everything automated and instrumented!
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Steve Demore S/V Doin' It Right Pasadena, MD |
#4
IP: 97.93.70.7
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Bill, I'm trying to recall for sure but can't swear to it.
800 RPM engine warmed a few minutes about 18", I do remember I would loose about 1" if the alt was working hard. Dave Neptune |
#5
IP: 24.152.132.140
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I'll take readings tomorrow. Per Dave's suggestion I can provide a number with and without alternator load and can specify what that load is. The carb in place has a fresh rebuild too.
edit: test done, a hair over 17 in. Hg @800 RPM. Batteries fully charged so alternator load was negligible, like 4A.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others Last edited by ndutton; 12-16-2018 at 03:43 PM. |
#6
IP: 50.35.34.141
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I almost voted 'don't know,' and I'm far away from the boat until spring, but my best recollection is the needle was a little to the right of vertical, which is 16 or 17. In gear at 1800 rpm it reads about 8, as I recall. That number goes up with a clean bottom.
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#7
IP: 71.206.91.77
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800 RPM - 19”
1500 - 13” 1700 - 11” 2000 - 7”
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-Jerry 'Lone Ranger' 1978 RANGER 30 |
#8
IP: 97.93.70.7
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Jerry, those numbers other than idle are terrible if not in gear. If in gear their great for a direct drive.
Under load with a clean bottom and Indigo prop my numbers were close to yours posted. My "cruise" speed was set with the Vac gage and my RPM's would indicate how clean or out of tune the engine was. When all was good 8" of vac would give me 2100 and my temp was always rock solid at 130*. This would yield about 6.4 kts in calm water with my E-35MkII and I was always towing a 10' hard dinghy. Dave Neptune |
#9
IP: 137.103.82.194
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Today at idle was 15 inches.
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#10
IP: 71.206.91.77
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Quote:
(I have to confess over a year ago) I'm not currently at my boat. (Sitting in the FL Keys)
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-Jerry 'Lone Ranger' 1978 RANGER 30 |
#11
IP: 137.103.82.194
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I am feeling under-vacuumed How do I get my number up?
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#12
IP: 192.186.122.174
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Bouncing right around 15 late summer - early fall when I first installed the gauge. Then I started fiddling and now can't even get an idle down to 800
only another 3-4 months before I can fiddle more... sigh |
#13
IP: 24.152.132.140
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Here is an excerpt of an article from Motor Magazine, August 2001 entitled Mastering the Basics - Reading a Vacuum Gauge.
Quote:
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
The Following 3 Users Say Thank You to ndutton For This Useful Post: | ||
#14
IP: 97.93.70.7
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Warning
Neil, that is a very informative post (#13) however it should come with a warning. Virtually all of the dancing of the gage is controlled by the vacuum and the dampening of the gage. Some gages are just to "dampened" to provide much more than a vacuum reading and some are designed for diagnostics with little dampening.
These dancing readings are mostly taken at very low RPM's. The dancing in a up & down pattern reading can be from plenum fluctuations at low speeds and will be symmetric in pattern if all is OK. A pattern of up & down that is not symmetric IE a big pulse is what you are looking for. Also where the gage is hooked up can influence patterns,, fortunately on the A-4 we have a good access port via the scavenge tube on the manifold. This port reads directly from the plenum which is where you want to be for fluctuations. When working on the dyno sometimes we would have a port on each intake runner to check for even flow through the manifold. Dave Neptune |
The Following 4 Users Say Thank You to Dave Neptune For This Useful Post: | ||
#15
IP: 137.200.32.54
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My vacuum gauge jumped all over the place at first. I transitioned from 1/4" rubber line through a restrictive brass fitting to the clear tubing and then ran that to the gauge. The fluctuations went away. Do not use the clear tubing the gauges come with all the way to the engine, when it gets hot it gets soft and will sometimes come off the fitting or melt. I used fuel line for the first part of the run, it seems to hold up quite well.
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#16
IP: 172.95.97.58
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Joe, using copper 1/8 tubing works great. Install it with a "vibration" loop and use a minimum of 2 feet for dampening.
Mine would idle all day and did for 7 hours once at 700 and I had the PCV valve installed too, no hick-ups just putted away. Timing 0*, EI,PCV,dist c-adv set too 17*@1600, J4J Champion plugs gapped to .042" and a slightly modified carb. Dave Neptune |
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