Tripletom's advice is right-on. In the USA, the EPA governs emissions and sets those standards - which Triumph has to fulfil in order to import. This resulted in a rather lean starting circuit set up, that requires careful use of the choke and a slight loss in drivability - the dip in and around 5k rpm is also blamed on the the EPA requirements by some, as apparently at this time it was a sampling region - maybe. Though it is believed that the UK bikes are the primary factory tune, various regions of the world do have restrictions ie USA and California - and perhaps elsewhere?! Either way US bikes do respond to an enrichening of the starting circuit - of which, in this case the fuel screws are a part of. This 'making rich' does 'add' throughout out the throttle range but most noticeably in the lower rpm's. At this point perhaps a few UK residents might want to say their piece as to how many turns their 'screws are at' etc.... - in the USA they come capped off, the cap has to be drilled out to get to the screws - yours shouldn't be capped if it's a UK one. If you've changed to a K&N, you'll find a little tweak might make all the difference - you'll get to know your bike in the process, get some good old man/machine bonding time and all that good stuff - perhaps a game of hide the weenie with the missus later, even!
Plastic off, Tank off, airbox off, a coil, pull the carbs, disconnect cables etc... - then clean and blow out - watch out for the little 'O' rings.
http://members.aol.com/cloudhid/carb.jpg Here the screw we are talking about is called the pilot (idle) mixture screw.
