Thanks for all the replies guys,really appreciated.
Got a Yuasa brand new battery in and a trickle charger installed too.
The bike started as if it were new,no problem at all,engine noise was totally fine...until you rev it up.
The sound is clearly (at least to my ear) from a loose chain grinding everywhere and it amplifies as the revs go higher.
I'm reading through the 613 pages zx12r manual to check point by point but my guess is a loose chain/bearing or something like that.
Is the rotor spun by chain or by direct gearing through the engine?
Also,where is that damn chain tensionner...can'T seem to find it.
Last minute detail: My bike is loosing oil,bit by bit. The mechanics changed the engine gaskets last summer and cleaned it and said he didn't find any reason for oil to be there but still,there is oil again. It's low on the left side,right in front of the shifter (
isn't it odd that's it beside the alternator..uh uh...)
I'm working on it today and when I find something,I'll keep you guys posted.
In the mean time,any suggestion is welcome.