Help with decel valve - 1973 2.0, Don't know if I have enough vacuum and it takes a couple seconds for accelerator to settle to idle. Options

[Downerman]

Base problem: Takes a couple of seconds for the RPM's to settle down to idle after I hit the throttle (@3500-4000) Rpm and then back to no throttle.

So, putting vacuum gauge on the small line coming from the step elbow that feeds the decel valve (again, the small line) I have at idle 10 hg. at 3500 I have 18.

With the bare decel valve on my bench, I apply vacuum to the small end, and blowing into the side tube (that runs to the top of the air box) it takes almost 20Hg to just barely get the air to move out the other large end of the Dcel valve (Valve opening). It would appear to me that the decel valve is never functioning and hence my problem. I have used some cleaner to loosen it up but that's where she's at now.

First off, do I have enough vacuum?
If so how many HG should it take to open the valve and is that adjustable with that nut on the decel valve?

Dave

[jcd914]

When you are revving the engine and then close the throttle your intake manifold vacuum goes way up. It is the high vacuum that opens the decel valve. The decel valve should stay open for a couple seconds maybe more if the high vacuum persist, such as decelerating in gear down a hill or such.
When the decel valve opens the manifold vacuum drops since it allows more air into the manifold.

The idea behind the decel valve is to allow more air in and reduce the manifold vacuum in order to reduce the sudden rise in fuel mixture (full rich) that the high vacuum causes. It is an emission device.

It also reduces the strain the sudden spike in manifold vacuum causes on the MPS diaphragm, although I doubt that was a consideration by VW/Porsche when they added the decel valve.

It actually sound like your valve is working as designed.

Jim

[Downerman]

When you are revving the engine and then close the throttle your intake manifold vacuum goes way up. It is the high vacuum that opens the decel valve. The decel valve should stay open for a couple seconds maybe more if the high vacuum persist, such as decelerating in gear down a hill or such.
When the decel valve opens the manifold vacuum drops since it allows more air into the manifold.

The idea behind the decel valve is to allow more air in and reduce the manifold vacuum in order to reduce the sudden rise in fuel mixture (full rich) that the high vacuum causes. It is an emission device.

It also reduces the strain the sudden spike in manifold vacuum causes on the MPS diaphragm, although I doubt that was a consideration by VW/Porsche when they added the decel valve.

It actually sound like your valve is working as designed.

Jim

Thanks Jim, I would agree..... although I did adjust it from 19 to 17Hg and it seems to be working better.
Side question..... is it common to have idle at 900 with the idle screw all the way in?



Dave

[914_teener]

When you are revving the engine and then close the throttle your intake manifold vacuum goes way up. It is the high vacuum that opens the decel valve. The decel valve should stay open for a couple seconds maybe more if the high vacuum persist, such as decelerating in gear down a hill or such.
When the decel valve opens the manifold vacuum drops since it allows more air into the manifold.

The idea behind the decel valve is to allow more air in and reduce the manifold vacuum in order to reduce the sudden rise in fuel mixture (full rich) that the high vacuum causes. It is an emission device.

It also reduces the strain the sudden spike in manifold vacuum causes on the MPS diaphragm, although I doubt that was a consideration by VW/Porsche when they added the decel valve.

It actually sound like your valve is working as designed.

Jim

Thanks Jim, I would agree..... although I did adjust it from 19 to 17Hg and it seems to be working better.
Side question..... is it common to have idle at 900 with the idle screw all the way in?



Dave

No. You may have a vaccum leak somewhere.