Originally Posted by AeroEngineer
Check to make sure all the connections between your carburetors and the airbox are on tight. It could be intermittently causing you to run lean and sap your power.
If you find you have to disconnect anything, remember to build the pipes back from the carburetor to the airbox, they'll stay on better that way.
Ahem. This suggestion was spot on, as it happens. We're doing our 5,000km service this evening and when we went to disconnect our airbox to check/change the air filter, we saw that even though the carb hose clamps were still in place, the hoses had popped off the carbs. We're still doing the full service but I wouldn't be surprised if that doesn't fix things right there.
(And yes, now I feel suitably chastened that this wasn't the first thing I checked. Just goes to show - a perfunctory visual inspection doesn't cut it!)