To test the sticky theory mentioned above, it's not even a 5-minute thing. Pulling the air cleaner almost takes more time.
Once it's off and you can see some of the linkages on the passenger side, a few quick sprays with Chemtool or similar cleaner, then a few judicious shots of WD-40 or similar lube will free it up in no time.
As long as it's adjusted properly and/or something's not bent, this quick clean-n-lube process does wonders for how it works.
There is a school of thought that you shouldn't use a lube, as it catches dust. Very true and a legit sentiment all the way. But in my experience, the trade-off between lubing and having to clean a bit of grit off of it in the months to come, is a good compromise.
With a new carb, the lubing isn't as needed, but with an older carb with potentially hundreds of thousands of miles and millions of cycles, the lube can be a real game-changer. But the other possibility is why I use something thin and relatively film-free like WD. The other spray lubes I like on other things, that leave a heavier film behind, would conceivably collect more crud from the air.
Give it a shot and see what happens.
If that doesn't work, plan-B would include checking the choke coil and other connections. But first things first.
Paul
