Hi Jon
Any carb jet work requires them to be removed so if you're not happy about doing that, no point in proceeding any further down the DIY route.
Has the bike been standing unridden for any length of time? Have you recently filled with fuel? I'm thinking maybe water in the fuel is one possibility. You could drain each float bowl to see if there's any cack inside but be really careful not to overtighten the drain screws when you refit them ... easy to crack the float bowl and they're not a separate spares item, so you can't buy a single replacement from Yamaha.
Another possible is a leaky float needle seat O-ring. A small leak past one of those would cause the float bowl to fill too high, in turn making the fuelling over-rich at part throttle openings. Rectification is a carbs-out job again.
Having eliminated water in the fuel, I'd try running some fuel cleaner through the next tank or two of fuel before delving into carb work. If the problem persists, dealer time ...
... however, before fixating on this being a fuelling issue, I strongly advise you to check the plugs and plug caps first. So many odd misfires/hesitations present like a carb fault but are actually down to the plugs.
Mike
