Thats a CT-240 cylinder you have, it uses the 6 bolt CR250 intake, so that's the gaskets you'll need to use on that, which is what I'd do instead of the RTV sealant. you do not want to damage that cylinder/piston
you do not need a new carb, that's a great carb for your setup, it just needs adjusted and tuned.
have you cleaned it properly ?
https://www.blasterforum.com/threads/how-to-clean-your-carbureutor.254/
air filter clean and oiled ?
tell us exactly what jetting is in that carb ?
pilot jet, airscrew setting, needle # and clip setting slot, slide #, and main jet ?
(50 pilot, 1.5 turns out on airscrew, CEL needle in middle slot, #6 slide, 155-162 main jet)
I'm going to assume that carb came with the CT cylinder as they sold them as a kit....
240cc top end, 36mm carb and right bend CT pipe, and should be closely jetted for that setup, but each engine is slightly different as well as temps and elevation which will effect jetting
if it's still leak free ? and you're having idle rev issues....
is the slide closing completely ?
idle screw not set to hold slide open too far ?
have you checked/set the float height and tuned the airscrew ?
https://www.blasterforum.com/threads/float-heights-and-how-to-adjust-them.50565/
https://www.blasterforum.com/threads/adjusting-your-airscrew-pilot-jet.51060/