When I open the throttle hard the motor misses a couple of beats - 1150 GS

Mostly it runs fine. I normally go at 120 to 140. It is only when I twist the throttle open suddenly that it misses. Most times missing only once, but sometimes it has two or three stumbles and then goes smoothly again. It does not matter which gear I'm in. When in neutral I can twist the gas and it picks up immediately - so it looks like it happens only under load. If I want to accelerate from say 100 to 140 and I do it gradually there's no problem.

I'd appreciate suggestions on where to start looking for the problem