I’m hoping someone with similar mods and carb can give you a suggestion on jetting. If the previous owner didn’t have any troubles then yes look for an obstruction in the exhaust canister, your header is easy to determine if it’s clogged. Removal and inspection is in order for sure. I don’t think the obstruction causes an air starvation more like a exhaust build up from the lack of an exit for spent fuel.
I ran a Keihin fcr35 and thevstock cvk34, So I’m only giving you suggestions that I know worked for me in the past.