Again, normal hardware store o-rings will swell when introduced to fuel. If it swells, it car come apart and end up getting sucked into the engine.
You will need to get o-rings that can withstand contact with gasoline.
It still sounds like there's an air leak somewhere.
Shining a flashlight into the carb and looking for "light leaks" won't give you much success in my opinion. The best way to find an air leak is to get the engine running, let it idle and spray starting fluid (in very small bursts) around the carb and intake manifold.
Concentrate on one area at a time and listen for the engine to rev up on its own.
If you shoot starting fluid at the intake to carb seal area, (for example) and the engine races up on it's own, you just found your leak. The air leak will suck the starting fluid into the engine and it will find the tinyest of leaks that you would never even be able to see.
Are you sure that you are actually choking the engine? You may have the choke on when you think that you have it off.
The choke on a cns carb works backwards from how a normal choke works. You open the choke for cold starting, and close the choke once it warms up. The "choke" is nothing more than a brass rod that slides up and down in it's own hole next to the throttle slide in the carb. The brass rod should be fully closed (down) for "choke off" (warm engine) and fully open (up) for "choke on" (cold engine).
When the choke is "on" (brass rod up) it delivers more fuel to the carb to richen the air-fuel mix for easier cold starting, rather than restricting the air flow to richen the mixture like a normal butterfly style choke.
my 73 Kawasaki 2 stroke 100 enduro has this exact style of choke set up on it, so i know how this style of choke works.