I have a Yamaha V-Star 650 that bogs down when I try to accelerate. My first thought was the carbs, but she revs just fine with the clutch engaged. I don't think that was the case the last time I had problems with the carbs. Could it be something else?
It could be a problem with the accelerator pump. This is a device on the carbs that detects when you are giving more throttle, as you would in acceleration, and pumps extra fuel into the engine. These can sometimes become non-functional because the rubber diaphragm in them deteriorates or becomes plugged.
Another problem could be a fuel line or fuel filter restriction. There is enough fuel for the engine under no-load conditions but when loaded it's starved for gasoline.
My last thought for now is that you have a clogged passage or get in the carb(s) that is also starving the engine for fuel under loading.
For a bike of this vintage, the carbs almost certainly need to be rebuilt. You didn't specify the year but it doesn't matter, carbs have been out-of-fashion for going on 20 years now.
If the acceleration is decreasing there could be other problems than the carburetor side. You can check the clutch plate because if it's old enough the clutch plates could lose its grip and lose traction with the drive plate. And if you did some modifications so that the total weight is increased that could affect the acceleration too. Finally check if the Tyre is in good condition. Check the air pressure and the overall grip of the Tyre if it lose traction from the ground