I have done everything to my bike 2009 xt660r pipes dna stage 1 and 2 snorkel removed kevs mods 02 and fuel mod new chain sprockets new Cush drives and bearings oil and filter new plug and still surging 0-40 mph above that it's fine goes great my bike is in excellent condition done 7500 miles I'm gutted and getting sick of it it's a shame as I love my xt