Pretty much what CRE said (and said well). The filter is there to prevent crap from fouling the flow control valve when the air flows inward (towards the diaphragm) when the throttle is off idle. The flow valve is like a check valve except it flows easily in one direction (towards the diaphragm) but flows with some resistance the other way.
The point of all this is to keep the throttle cracked for a second when it's released. Because the air flows out with a little resistance the throttle will remain open for a second as the air in the dashpot bleeds off. The dashpot is an emissions device. It prevents an HC spike when the throttle is lifted by providing a bit of air (from the delayed closing of the throttle plate) to burn the remaining fuel left in the cylinders. Otherwise the engine would go quite rich for a moment. It does anyway but the dashpot limits the spike.
You have the flow valve installed in the proper orientation. Since the filter is missing it may have ingested some junk and isn't "breathing" properly. What you should see when the throttle is opened and then released is a slight delay just as it closes. You can watch for that at the dashpot plunger or throttle stop screw. Or pop the valve off and blow through it. One direction should be easy while the other direction should be harder. If it checks out but you still see no delay the dashpot diaphragm itself may be ruptured although that's unlikely.
Since you've knocked the dashpot out of whack you might as well just back the screw off until it doesn't hit the dashpot and see if your problem goes away. If it does the dashpot, flow valve, or filter is at fault
Now that you've messed with the system you'll need to set it all up again. Warm the engine up then open the throttle to 2500. Pinch the dashpot hose. Upon releasing the throttle the rpm should settle at 2000. If not adjust the screw until it does. When you're done unpinch the hose and the rpm should return to idle. All the procedure does is use rpm as a way to set how far the throttle closes before the dashpot takes over and slows it down until fully closed. If that doesn't make sense RTFM. Course, you could also just remove it.
bluedragon17: Is English your native language?
