I'd definitely go with Johnj's recommendations. Can you post a photo of your carb boots (those are the rubber bits between the carb and the cylinder head)? If they are cracked at all (and if they are original, I'd bet a $1 they are), I'd replace them with NEW ones (if you can find them). You CAN temporary use a good quality silicone and go around them to help stop any air leaks, but really, they are most likely warn out.
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