In an effort to quiet down my after-market exhaust system, I have inserted a copper grill scrubber into the end of the muffler. I was also hoping to reduce the flow and help the bike run a little smoother. (She seems to prefer to run with the choke on a bit.) If the bike is not running poorly with this added obstruction, is there danger of damaging the engine from the increased back pressure? It does seem that the stock exhaust provides quite a bit of back pressure.
If you consider the restriction that Mr Yamaha put into some headers - see http://www.ttr250.com/detail+of+restrictor.jpg - I doubt your grill scrubber would cause a problem but, if the bike runs poorly with it fitted, you may need to look at an alternative. Depends on how "open" the mesh on the scrubber is I guess