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Old 03-12-2009, 08:09 PM
Paul K Paul K is offline
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Vacum gauge at zero.....

I have a '72 Ranger with an Atomic motor. We took it out to fish off of this past Sunday, and during the first putt up the coast, there was a strong gas/oil smell in the cabin, to the point where we all had to sit outside. When the motor wasn't running, the smell went away. The oil pressure is at a steady 40lbs, the water temp. is at a steady 140 degrees, the amp gauge reads about 2 volts to the positive, and the vacum gauge reads zero.

First, what is the vacum used for in this application, and what should it be reading?

The boat is in So Cal, in San Pedro.

Paul K
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Old 03-12-2009, 08:18 PM
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msauntry msauntry is offline
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Check your oil level and see if it is unusually high and smells like gas. If you have a mechanical fuel pump, the seal may have leaked. This would allow gas from the carb to mix with the oil in the crankcase, which would then get vented to the outside through the crankcase vent (tube above the carb flame arrestor). Check the carb for obvious leaks as well. Be carefull of sparks and run the blower when working on it.

Haven't seen a vacuum gauge mounted on an a4 b4...
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Old 03-13-2009, 08:24 AM
rheaton rheaton is offline
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You might want to add an inline bulp fuel pump in the line. This will allow you to preasurize the system and hopefuly detect any fuel leak.
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Old 03-13-2009, 10:02 AM
Dave Neptune Dave Neptune is offline
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Smile Vacuum

Paul, the vacuum guage tells you how hard the intake manifold is working. The guage should not read "O" unless the engine is off. At idle you should show around 15-18 inches of vac. As you increase the load on the engine (throttle up) in gear the guage will drop towards zero at (your affective) full throttle. If the guage isn't moving it could be the line that feeds it is leaking or even missing. If you get the guage working it will prove to be very valuable for tuning and knowing how the engine is performing. It is a good diagnostic tool for a gas engine. We'll need a little more info to figure out the gas smell, then we can show you how to utalize the Vac-guage. I to am in So Cal and headed to Newport for a 30 plus "Wagon wheel raft-up" for the weekend. I'll chime in again on monday when I have the time to explain the use of the Vac-guage for tuning and crusing!

Volador E-35MkII 1970 original A-4
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Old 03-13-2009, 02:31 PM
tenders tenders is offline
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I would be interested to know how/where to install a vacuum gage onto an A4.

Hey, Don has no kit for this already??!?
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Old 03-16-2009, 12:34 PM
Dave Neptune Dave Neptune is offline
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Thumbs up Vacuum guage

tenders, I installed mine at the "scavange line hook up port" on the side of the intake manifold. All I needed to do was install a Tee fitting and run the tube to the guage. I am truly amazed that more are not using a Vac/guage as it is the only way you can measure what the carburator is feeding the engine. I spent a few years working on a dyno and a flow bench while building racing engines anything from cosworths to big blocks single cylinder to an old V-16 (Caddy) and even a few "Rotaries". In measuring a gain in performance you need to be able to measure what you are "feeding" the engine at a given rpm to see if you made a gain with what ever you changed. Otherwise all you can evaluate is how much power you are making and not how much power you gained at a specific carb feed rate at a given rpm. The Vacuum guage is the first thing I installed when I bought mine.
I usually cruise with my engine by increasing the throttle to a specific Vacuum reading of 7" which gives me hull speed. When the speed levels off and I am at 7" of Vac. and I am at a lower rpm than before I know something is amiss dirty prop or a tuning problem is beginning to show up. If I make a modification or adjustment and gain a hundred rpm or so at the same Vac value I have made a gain or visa/versa. It is especially valuable to those who tinker to make gains in power or fuel consumption, otherwise you really don't have a baseline to measure your gains since you can just apply a little more throttle and get the same rpm. The engine should perform the same at a given rpm and vac/value or something changed via your tinkering or something is going amiss.

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