Your over tightening it. best thing I have found with this is to apply anti-seize then tighten it finger tight, and 1/8th further with wrench or quarter.
To remove it. go to local auto parts store or discount store (wal-mart) and buy a can of "PB BLASTER"
Its the best there is at getting stuck things unstuck.. You can put some in a Styrofoam cup, in 30mins.. there will be none in the cup.
Just sprey some in the top crack and around in there wait 10-15 mins and try it again.. if it still doesn't work.. you stuck it good, and you'll need to get your wrench out, and get more torque on it. by using vice grips, open end wrench something to get more torque.
The problem I see with stuck chokes is people over tightening, and not removing them to oil etc.. instead the threads rust together.
If you still cant get it.. here comes drastic measures.
MAKE SURE YOU REMOVE ALL THE OIL.. Get one of those $5-$15 torches. there small handheld.
gunsmith trick Heat the barrel ON THE INSIDE SLIGHTLY.. for maybe 15 sec.. all the way around the barrel. try it if it doesn't come out add 10sec of heat time. DO NOT DO THIS ON THE OUTSIDE OF THE GUN. Eventually it will come out... I have had to resort to it once... but PB BLASTER usually works.
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