20hp Tohatsu will not idle without choke

Hello all,
I have a 2009 20hp Tohatsu that I tried to get running for the season after sitting idle for about 18 months.
When put into storage, I used fuel stabilizer and also ran the engine to use up all remaining fuel then fogged the engine.
The engine started up no problem but will not idle without using the choke. When using the choke, it will idle rough but it will idle. I then slowly push the choke in and the idle will raise and the engine will smooth out then stall.
I pulled the carb and intake off and the carb is spotless inside with all jets clear. The intake gasket was wet through the entire width of the lower section of the gasket.
That is the only thing I could find.
Does anybody else have any ideas?
Also, I did not remove the plate on the top of the carb, only the lower bowl.
Thanks for any help that you are able to give.

Your symptoms have the classic ring of a low-speed varnishing. Completely disassemble the carb (including the top cover, jets, and emulsion tube nozzle). Submerge all non-rubber bits in carb dip for 4 hours. Blow out all passages with generic carb spray. Reassemble, checking float height. 99% sure that if you clean the carb using that regimen, you will run a lot better. In the future, religiously run the carb dry at the end of each and every day.

Thanks for the information pvanv,
I will heed the part about runing the carb dry for sure.
I ended up taking the carb all apart and it was spotless. I could not find as much as a little grain of anything in there.
I had ordered new carb mounting and intake gaskets so I put everything back together and it runs better now than it did when I first purchased it. I believe I may have had an intake leak from the very begining, although looking at the plugs I did not see anything strange.
I also put new plugs in as long as I was right there.

Anything is possible, though intake vacuum leaks are rare on those. The varnishing I was referring to would not be visible, as it would be in the internal passages. You may have washed some away by spraying things out. Glad it all worked out for you!