I've narrowed down the bikes for my son to the xr70 and ttr 90. The ttr is pretty hard to find used, so the honda looks promising. Are there any changes that have happened within the last few years that would make one year better than the other? I know Honda changes the xr as often as Kawi changes the klx, but just thought I'd check in the event anything major has been improved.
Sorry about that! The 2000 model is the same as the '99.
It's really not a big deal about the exhaust system, since there are many aftermarket options, from complete systems (for modified engines) to the Thrust Chamber that Powroll makes. Any of these options will make the 99 - 2000 models run as well as the newer ones.