340 Idles at 3200 RPM!

Take the carb off, Hold the primary throttles closed with one hand, and keep it closed,flip it upside down,and visually see if the throttle blades are hung open.
If they are, go to the choke mechanism and manually reposition the fast idle cam so that the throttle now closes. Again, keep the throttle closed and flip it over for inspection.If still hung open, back off the curb idle speed screw, until the throttle is completely closed. If it will not completely close, remove the S link from the pump-arm and check it again.If it still will not close check the linkrod to the secondaries; the secondaries must be closed up tight. Is it possible you installed that link-rod wrong.
You may have to reposition the fast idle cam every time you flip the carb over.
If it still won't close, I give up. Did you remove or loosen the butterfly valves?
>But when you finally get it to close all the way, you will need to readjust the curb idle speed screw. First screw in your mixture screws all the way, but lightly seating them.Next go find the transfer slots. These are right beside the idle discharge ports, with the mixture screw tips now sticking out of them. There is one vertical slot in each primary bore.
Then crank the speed-screw in to open the throttle blades just enough to expose those transfer ports; continue adjusting the speedscrew until those ports look like little squares. Now back out the mixture screws about 2 turns.
After you figure out which little bugger was the guilty one, fix it and reassemble everything. Then one final check; reposition the fast-idle cam to off,hold the throttle closed, and flip it over. The secondaries should be close up tight, and the primaries should have the Transfer ports exposed like little tiny squares.Hold the choke off and exercise the throttle arm a few times, and be sure it returns to the curb-idle screw each time.
Now it's ready to be reinstalled.

After that it is bolted back on, make sure all vacuum ports are plugged or properly hooked up, especially the PCV hose, and the vacuum booster.And that the fuel line is properly fitted and secure.
Next pop the metering rod retainer plates and make sure the rods are going up and down properly.
Make sure the choke electrical wire is hooked up and that there is power in the wire, with the ignition key in the run position. After the engine is running and you have tapped it down, you will have to adjust the fast-idle speed,to not be racing.Every engine is different and it is somewhat dependent on your timing, but I don't care for an engine warming up on the fast idle cam at much over 1200 rpm.
Good hunting!