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I've never had a car with a vacuum gauge before.  Now that the 63 R1 is up and driving more I wonder if I have an issue.  When idling the gauge bounces all over and then at any other rpm it is steady.  Is the idling bounce an indication of some sort of problem or is it just normal operation?  Thanks

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It should stay fairly steady unless your idle is not even. I think these are basically pointless unless you have a supercharged car to see boost pressure. 

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The first thing to do is disconnect your dash gauge at the engine connect a known good vacuum gauge. See if they behave the same. Then take a look at an old 1935 to 1965 Chiltons manual, look under engine diagnosis.You will find a good diagnosis chart. Vacuum gauges when you know how to use them are very accurate and useful. They can be used to set ignition timing when balancer marks are innaccurate. They can also help diagnose a multitude of engine problems.  Google "engine vacuum diagnosis chart" and you will see what I mean. Look at the chart pay close attention to a good gauge and you will be surprised what you find out.

                                                                                                                                                                    Best of luck, John C.

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As an added note vacuum gauges were factory installed in many cars and boats to help show peak fuel economy. Not just blown cars.

                                                                                                                                                                     John C.

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3 hours ago, John C said:

The first thing to do is disconnect your dash gauge at the engine connect a known good vacuum gauge. See if they behave the same. Then take a look at an old 1935 to 1965 Chiltons manual, look under engine diagnosis.You will find a good diagnosis chart. Vacuum gauges when you know how to use them are very accurate and useful. They can be used to set ignition timing when balancer marks are innaccurate. They can also help diagnose a multitude of engine problems.  Google "engine vacuum diagnosis chart" and you will see what I mean. Look at the chart pay close attention to a good gauge and you will be surprised what you find out.

                                                                                                                                                                    Best of luck, John C.

Rather than disconnect the factory gauge, I would hook up a test gauge in parallel to compare the two.

I do recall several car manufacturers using vacuum for fuel economy indicators. 

The gauge on the Avanti is a vacuum and pressure gauge which is normally used for blown cars like the original R@ and R3 cars

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18 hours ago, John C said:

The first thing to do is disconnect your dash gauge at the engine connect a known good vacuum gauge. See if they behave the same. Then take a look at an old 1935 to 1965 Chiltons manual, look under engine diagnosis.You will find a good diagnosis chart. Vacuum gauges when you know how to use them are very accurate and useful. They can be used to set ignition timing when balancer marks are innaccurate. They can also help diagnose a multitude of engine problems.  Google "engine vacuum diagnosis chart" and you will see what I mean. Look at the chart pay close attention to a good gauge and you will be surprised what you find out.

                                                                                                                                                                    Best of luck, John C.

Thank you, I'm going to do this.

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