Hey folks, looking for ideas / help.

Spent the weekend playing spanner with the bike. It's the old pig, 1987 CBR600 F. Has a bit (a lot) of a rattly cam chain. Got valve covers off inspected the cam chain and sprockets, looks in pretty mint condition (Cam lobes themselves are a little worn though). Took Cam Chain Tensioner out and it's poked (leaky as) gave it a clean and whacked it back in until the new one arrives. Interestingly that has (temporarily) sorted the rattle. Changed oil, filter and flushed the radiator while i was at it.

So here is the question. On my way into work this morning, noticed the bike has developed a pretty wicked flat spot around 3000-4500 rpm (rpm range that the cam chain used to rattle). Any ideas as to why, and if so what does one do about it??

Cheers