The hose I'm talking about starts on the top of the left cylinder head and runs to the carb's if I remember right. If you pull the left side lower cover you will see it. I changed mine with the same hose from my old motor that I had, but that hose has to make a U turn and was made with that bend in it. I would buy OEM if I could find a new one. It's a good place to start looking for your Idle surge.
Similarly, on the right side of the bike (center cylinder, about an inch above the valve cover) is a screw... It's typically removed/replaced with a brass spigot when connecting a Mercury Carb Balancer.
Anyhow, if that screw (or the capped spigot) is missing/loose, then you'll get a vacuum leak there too.