The benefits of a Vacuum Gauge!!!

[PKRWUD]

I answered a question about vacuum and what it was good for a couple years ago on this board, and in the past 24 hours, I have seen several posts that would benefit from it, so I dug through the archives and found it. Here it is, and I hope it helps someone.

posted 09-29-1999** **** **
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Chipdog-Five did a good job of covering the basics. Take note. The vacuum that is created in a normaly aspirated engine (one that is not blown or turboed) also gives you a great tool for diagnosing engine problems. Just about any internal engine problem can be identified with a vacuum gauge !!! I'll teach you some of the basics:
1) A steady reading of between 17" and 22" is considered normal for a stock motor.
2) A low but steady reading between 10" and 15" would be caused by retarded ignition or valve timing, or low compression.
3) A very low reading between 4" and 9" means you have a vacuum leak.
4) If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring.
5) A gradual drop in reading at idle means you have excessive back pressure or partial blockage in the exhaust system.
6) An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve.
7) A reading where the gauge needle drifts anywhere between 12" and 22" indicates that your idle mixture is unstable. This is more common on carbureted motors.
8) A high and steady reading indicates that the ignition timing is too far advanced.
9) If, when you quickly close the throttle after running at 2000 rpm for ten seconds or more, the gauge needle DOES NOT jump two or more inches above what it is at idle, your piston rings are shot.
10) If the reading at idle is lower than normal, but the gauge needle fluctuates three inches on both sides of normal, your valve guides are excessively worn.
These are but only a few of the things you can learn about the condition of your engine with a vacuum gauge. Keep in mind that a blower or a turbo will create a false reading because the boost they create offsets the vacuum reading.

posted 09-30-1999 **** **
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I love using a vacuum gauge. Here are a couple more "old timer" tricks that you can use on a non computer controlled, carbureted engine:

1) To adjust the ignition timing to the best spot without a timing light, just hook up a vacuum gauge to manifold vacuum and advance the timing, slowly, until the needle on the gauge stops going up, then retard the timing until the needle drops 1/2" on the gauge.

2) To set the idle mixture on a carbureted motor, basicly do the same thing, except with the mixture screws. Richen the mixture until you get the highest vacuum reading you can, then lean it out until the needle drops about 1/2".

Enjoy.

Take care
~Chris

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