My 850 has had a few issues off idle. First was a stumble or stall when trying to roll away from traffic stops. Turned out to be worn needle jet and or needle. Later, had cough/misfires happen about 1/3 to 1/2 throttle open, progressed to be more severe/frequent over a few hundred miles. Turned out one main jet was coming un-wound from carb body, which makes the whole needle to jet opening out of whack.
Very recently had hard starting, then later dips/loss of power while highway cruising. Turned out one carb manifold have become undone from head, insulator gasket shifted etc, so loads of un-metered air enter one cylinder. Check for any air leaks and ensure the rubber balancer tube on the inlet manifold spigots is well fitting, not leaking.
