Hi woodsy, thanks for the wr/yzf info, it helped me get a bettter deal on a used wrf localy.
to answer your question... this is for a xr250 but it all aplies to the 400 also, i have the white brothers pipe, cleaned out the header, K&N airfilter, kevlar clutch and heaver clutch springs also a 277kit. it doesn't cost all that much to mod these things and i got good results from everything, espesialy the clutch. only the big bore kit will effect reliability, instead of 20years on a piston i might only get 5:)
yes a ktm 400 would be better but their are downsides to the ktm, even with a new xr400 and the mods i have and bars the bike could be had for right at 5k, the ktm would be $1500 more at least. The ktm is proving to be reliable but i see 20+ year old xr's out on the trail so you know the xr is reliable. i don't think you can buy a bad bike these days, they are all so good.