Welcome on board Angela and you sure found the right place for all of the info that you seek!!! And you will also appreciate the non technical talk that they use here, so even I can understand. The main problem with the XTs is that they are very restricted both in intake as well as exhaust, to meet the EU rules about noise and emissions I guess. So I fitted a set of Leo Vince pipes (cos they save alot of weight and allow the bike to breathe much better) plus removed the snorkel and fitted better air filters plus the Kev fuel mod. Total cost perhaps 300 quids and the bike goes sooooooo much better. Have fun!!!

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(Now sold on, sob) 2011 Blue XT660X with gold wheels, was 26,500 km.
Engine mods: K&N Stage 1 filter, DNA Stage 2 filter, snorkel removed, Kev fuel mod fitted.
Plus: smoked Puig screen, Yam aluminium sump guard, Yamaha / Acerbis handguards, Givi Trekker aluminium side cases, Leo Vince X3 cans plus Kev front fork mod and Fender Xtender. Just fitted Michelin Road Pilot 3 tyres.

SOLD the XTX for a Super Ten 1200. And just bought a Raptor 700 so staying on here for some tips....