Loosen the draw bar (“pinch bolt”) so it’s loose. Try twisting the carb clockwise to break loose, then work it both ways while pulling on it and it should come out. If the draw bar was overtightened, it will deform the carb body a little and it will bind in the bore. Twisting and pulling will remove it. Why do you say the carb isn’t working and needs replacement?

Idling an engine for a minute is no good. If your carburetor is adjusted properly, it should slightly load up - but only enough that after a 15-20 second idle period the engine will still clean out and throttle up without flaming out. After a minute, the crankcase has accumulated a lot of raw fuel that pools up. When you throttle up, the excess fuel douses the plug and puts the fire out.

If the o-rings on the needle valves are good and the throttle operates smoothly, there is probably nothing wrong with it. If the engine will start and run with the current needle settings, I wouldn’t change anything and just run it and fine tune it. As for fuel leaking around the needle valve, make sure the needle assembly is screwed into the carb body snugly. There are sealing washers on either side of the fuel banjo fitting. If tightening the needle holder doesn’t cure the leak, replace those sealing washers.