Bike is stock except for Dellorto SHA 14.12 carb, currently with a 58 jet. Bike runs well overall except has started having this issue lately - the bike will get up to 25 just fine but then kinda struggles around 28-30 and there an intermittent buzzing/grinding noise (hard to explain) seemingly coming from the top end of the engine.
Just tried fully cleaning the carb and not much difference. Exhaust is reasonably clean I think. The bike used to get over 30 pretty easily and wasn't making this noise. Like I said it only does it as it approaches max speed, everything else is pretty normal. Any ideas?