Your dealer probably meant that it would be a huge waste of money to try and turn a 400cc engine into a 500cc engine instead of just buying a 500. For some strange reason a few people get a 400cc machine and want to trick it out to compete with machines of larger sizes 500, 600 800 and so on.

After your machine is broken in well, probably 500-1000mile range, you could try some after market modifications to adjust the machine to your individual riding style. Quicker pick-up, or more low-end grunt, etc.

What you have to look at is the percent of overall power increase you would get for the amount of money you would spend. Personally, spending $1500 in mods for a 1% or 2% increase is not worth it. Especially since most mods (jetting, muffler, air filter) increase fuel consumption and fuel is kind of expensive these days.

Put some miles on your machine, then if you want to mod the machine but don't buy them from him as he must not want your business too bad. It is your machine, you paid for it, you can do what ever you want to it. Just do a little research into the specific gains of the mods you wish to do first to see if they will do what YOU want.

SJ