If it won't hold a 'tune' and is running lean, you have an air leak someplace.
Check the carbs, air tubes and connectors by spraying those areas while the bikes running. If theres a change, you have a leak and the rubber carb connectors do need replacement every decade or so.
+1 on the throttle shaft o-rings. If they need to be replaced, several of us here can walk you through that repair. It sounds like a bigger deal than it is and it's something that most owners neglect to do, even if they rebuild the carbs.
Check and come back with your results.
Hate rots the pocket that carries it.