reread your post again, sounds like you definately have an air leak, especially because the choke half in, gets a response, check all possible air intake joints, but could be a crank seal from what i've been readin on here???
below is what i first wrote, gonna leave it in case somthing there helps ya
at least your getting some response, did you clean the new(old) carb, sounds like the float may be sticking?? when no other adjustment will bring the idle down?? or an air leak, get some wd-40 or start fluid and slowly spray around everything air related, if it revs you found it
make sure the slides in the right way, pin and groove line up,and the plug may not matter???, gap it right, just make sure it doesnt have a longer neck/threads so it doesn't stick down in too far and hit the piston, in my old blasty i ran a b9 sumthin, it was supposed to be 1 range hotter??? thats what i was told, but i had that thing in there for years and never fouled or gave me sh*t???