I've been following this thread and doing the suggest repairs/replacements. Temp sensor in the water pipe. Checking all vac. lines for proper connections. It's been weeks since the carb was off so I can't remember seeing the bent or kinked vacuum lines. Gad, I hate to pull that off again. I have not checked the plugs, but will tonight. The bike has been setting for 6 yrs. Carbs rebuilt, lots of little things repaired and replaced throughout the systems. It runs much better than a few month back but now has this surge at low throttle, as the core of this thread is focused on. Here's a video I shot tonight of the bike fully warmed up, throttle set to 2k rpms and held. No choke. Really frustrating to say the least.
Thanks for the help on this.
That sounds awful! First, I suspect the fuel mixture is not right. Did you sync the carbs and also perform adjustment of the idle mixture screw?
Also sounds like it is misfiring on 1 or 2 cylinders. Have you checked the plugs and wires? And also the C57 electrical connector on the harness above the right radiator cooling fan?
That sounds like an obvious misfire going on. Leaking vacuum lines will also cause problems, but in my honest opinion, based on what I'm hearing, you are having a fuel mixture issue, along with possible fouled plugs. I'm learning that the nickel plated plugs on these machines do not last very long.