WRD valve cylinder not "air tight" ?

[awolff280sl]

For FIP gurus:
My car idles when warm at 850, but I've come to realize that the idle air screw is turned all the way in, ie. essentially completely closed. As it turns out, the other soure for idle air is my WRD, which is "gently" sucking air. I know that the thermostat is working and that the cylinder that it pushes down is sliding well. I believe that my washer/shim set-up allows the thermostat plunger to push the cylinder down enough to cover the air inlet when hot. The car idles at 1200 when cold and gradually drops to 850 as it warms. The amount of air that it sucks when warm is just a fraction of what it sucks when cold, but it appears to be enough to supply the air for idle because if I cover the WRD air intake, the engine dies.
What I think is happening is that even though the cylinder is covering the air inlet, air is "leaking" around the cylinder. Fortunately, it's not bad enough to seriously affect the idle, but like I said, my idle air screw is all the way in.
Is there any way I can verify that the cylinder is really covering the inlet? If air is leaking around the cylinder, can anything be done for it?

[al_lieffring]

I was taught back in the 70's that the way to test if the warm running thermostat was closing off completly was to remove the air filter from the injection pump and hold a cigarette by the opening and see if the smoke was drawn into the cold idle air valve. No one I know smokes anymore, I never did.

I would say that when working properly, covering the air intake should drop the idle by 100 rpm or less after the engine  has warmed up.

It is possible that a faulty thermostat is moving but not enough to completly close the valve. Another thing that I have seen is the water passages are partially closed off not allowing enough hot coolant circulation to get the thermostat up to temprature. Check the passages where the coolant circulates through the throttle valve.

[awolff280sl]

Thanks Al. My WRD housing gets very hot, I don't thing that's the problem. I've tested the thermostat in boilng water and it seems to work well.
Maybe I'll go under the assumption that the cylinder isn't getting pushed down quite far enough. To test this theory I'll start shimming the top of the cylinder and see waht happens.
Any one happen to know the size of the shims (inner and outer diameters) that sit on top of the cylinder?

[hands_aus]

I think you need to sort out the reason why the idle air screw is not open when the Venturi is closed.
Perhaps the venturi has been adjusted open by a mechanic to provide an increase in idle speed.
Almost the first thing in The Linkage Tour is to check that the Venturi valve and Injection pump arm are both on their stops with the linkages disconnected.

You said that you already tested the WRD for air leaks and believe that the valve is leaking. I think you are right.

When the Inj Thermostat is fully open at normal temperature the valve should have shutoff all additional air. However most leak slightly.
If the rest of the idle air supply is adjusted correctly the very small amount of air coming through the WRD should not be enough to keep the engine idling at 850rpm.

There are small washer type shims in the top of the valve. You could buy a selection of washers or raid your parts bin and find some that will fit.

If you don't know the age of the thermostat then maybe suspect it.
When I replaced mine there were differences in shape which I had to allow for. I think these changes have been discussed on here.

[awolff280sl]

Bob, thanks for your input. I had previously replaced my thermostat and did have to drill out the thick washer to get the new-design thermostat to sit properly. I am now proceding under the assumption that the thermostat plunger is not quite long enough when fully warmed to push the valve just a mm or so more across the opening of the air intake.