Wait, you have an RC51 and just bought a 750 as a track bike?
MARRY ME!
jk
It does sound like your chain tension may be a little too tight, on decel the weight shift forward would stretch the chain more, which is why you wouldn't hear it on acceleration. As for the bike not clicking into gear, that's actualy not uncommon, the shift dogs are slightly overbuilt to withstand wear better, and sometimes they will aling and prevent the bike from clicking into gear, all it takes is slipping the clutch very slightly to get them to mesh. I would be much more concerned about the transmission if it jumps out of gear. I hope this helps, now about that marriage proposal....
