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Deceleration Valve Help

I have a 1980 911SC with a question about the deceleration valve. Mine is capped off. Is this correct? According to the Bentley Manual it appears there is a vacuum line running from the valve up to the throttle body. Any and all help is appreciated. Thanks

Last edited by TracyC; 09-07-2019 at 03:04 PM.. Reason: Adding a picture
Old 09-07-2019, 02:54 PM
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It's an emissions device. A lot of them got capped because people didn't like how they tended to artificially hold revs high when you snapped off the throttle and created a high vacuum. Very common. You could reconnect it and see if you like it or not. As the valve ages it tends to create high idle problems too. I have a "new" old stock one connected to my car and sometimes it sticks open. They are problematic.
Old 09-07-2019, 03:19 PM
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Originally Posted by gazzerr View Post
It's an emissions device. A lot of them got capped because people didn't like how they tended to artificially hold revs high when you snapped off the throttle and created a high vacuum. Very common. You could reconnect it and see if you like it or not. As the valve ages it tends to create high idle problems too. I have a "new" old stock one connected to my car and sometimes it sticks open. They are problematic.
Gazzer, I sent you a PM
Old 09-07-2019, 04:09 PM
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Decel valve.........

Quote:
Originally Posted by TracyC View Post
I have a 1980 911SC with a question about the deceleration valve. Mine is capped off. Is this correct? According to the Bentley Manual it appears there is a vacuum line running from the valve up to the throttle body. Any and all help is appreciated. Thanks


Tracy,

A good working decel valve is NC (normally closed). When the engine creates too much vacuum (approx. 22Ē Hg) during deceleration, the decel valve opens up and reduces the vacuum. If you disable the decel valve by plugging the vacuum line that operates the valve, your motor will lose the ability to release the excess vacuum inside the engine.

What most people donít understand about a decel valve is how it operates. The vacuum line to the nipple of the decel valve is the one that controls the opening of the valve. So you have to check if the decel valve is good or not with or without vacuum. There is a very simple method to test your decel valve if it leaking or not. If it defective or leaking, it could be adjusted to make it seal.

Tony
Old 09-08-2019, 07:19 PM
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