Your lower or idle jet is clogged. Like Pochop said...maybe something floating in from the tank. Anyhow...pull that external screw off the carb and spray carb cleaner in the hole and it should unclog it. If not, you may have to take the whole carb apart again. I would go dump an entire bottle of Seafoam into the tank after you get the carb jet unclogged and it will help minimize/prevent re-occurances. I know that much Seafoam is a bit of an "overdose" but it will burn just fine and won't hurt anything.
whats the year/make/model?
i'll find a layout of the carb parts and point out which are what and you can go from there..
it will have an idle circuit that may be completely closed (either a low speed fuel or air screw)
after that would be the pilot jet (which operates from idle to 1/4 throttle mainly)
Its a 2003 yamaha big bear 400cc
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Take it apart and blow out the ports......If you need help just call me , you have my# and I will come over and help you.
Orange circle is low speed screw.. to adjust this you turn it in all the way until it stops, don't over do it turning it in.. then you turn it out to spec (i'll have to dig for specs, but start at 1 1/2 turns out)
green circle is the pilot jet, its got a very very very tiny hole in there. its easy to clog and hard to unclog without proper fine wire
also looking at that carb i'm sorry to tell you that they are a pain in butt.. there is a few common issues with them when they sit for to long the gas eat away the rubber diaphragm on top of the slide, cracks or holes are problems..
try the low speed adjustment first, then take it apart again and check pilot.. if neither then check rubber seals and diaphragms
