Do you know the previous owner and if so did they make any changes?  Is it a stock muffler?  Has it been re-jetted?  Does it also stall while at idle for a couple minutes, or can it sit at idle for a while without stalling?

Have no fear - this list can help you figure this out!

If it's been sitting for 3 years that carb could use a good cleaning top to bottom I bet, say if the the slide in the carb is dirty/sticky it will sure do that as it would drop back down and close off the main jet, there's a vac hose
that runs from the right(starboard) side of the carb to the back side of the fuel petc0ck, be a good idea to take it lose and see if it has gas in it - another not too nice thing if it does.

Me I'd pull the silde and clean that area real good.

Welcome to the zoo!

If it is  running so very rich and there is no problem with the air,there are 2 possible reasons - either it is getting too much gas thru the intake manufold, either there is a lot of gas in the oil.
If You haven't replaced the oil- do it.
Check the vac. line for gas leak in the intake manuf.
Usually the reason is the carb. There is an O-ring between the brass float valve and the carb. body and this O-ring starts leaking. Remove the float . Unscrew the little screw that holds the brass piece. Pull the fl. valve out and make sure everything is clean.Replace the O-ring. Assemble back and try.

Topi I see your profile lists you as being in Los Angeles....I'm over in Torrance and have had a lot of recent experience with taking these carbs apart, cleaning (boiling) them and getting them back up and running (So far a Savage and 3 Intruder's carbs with rejetting on a couple as well)....

Anyway if your stuck let me know and maybe we can get this resolved for you real quick like.

so the slide had been greased?

boy howdy that ain't gonna work!