GL1000 revs slow to pick up from idle when throttle cracked open

[Speedbrace]

Anyone have an idea as to why my 1976 GL1000 revs are slow to pick up from idle when the throttle is cracked open. There is some hesitation before the revs increase, but there's no hesitation when the revs are above idle and the throttle is opened.

Could this be sticking slider valve(s)?

 

[pidjones]

If the carbs are clean and well-adjusted, you might want to look at this: How to Cure "Off-Idle" Flat Spot | Randakk's Blog