Hi new to the forum, just bought a New RS 50 and as of yet it is still restricted. I have been quoted by a mechanic £490 for the derestriction. This includes new arrow exhaust, new carburetor and new chain and sproket's. Does this sound about right? I was going to just derestrict the standard exhaust and rejet the carb but was told this was harmful to the engine, is this correct?