Has anyone located a source for this rubber bit that the carb attaches to? CMSNL does not even show it as a part number. Mine is hard as rock and has cracks developing at the carb mount end.
There is a guy who pops up on this forum every once in a while and 3D prints parts. He's printed air cleaner parts for, I think, CT90's. Too bad I can't recall his name. Maybe someone else can. He might be able to help.
Try using a shock rubber boot from a car. Used once off my aftermarket performance shocks I had on a jeep. Get a ribbed one. Small opening for carb. Trim at large rib for other end.
Not helpful for you situation (because of the cracking issue), but I found that soaking for 48 hours is a mixture of one part Wintergreen Oil and 3 parts Rubbing Alcohol was successful in making my pretty stiff rubber parts soft and pliable again. Just posting for reference for others.