OMG..... Why 612 cc ? THESE ARE ANTIQUATED DINASORS ! They go SLOW ! I've owned my 01 500 seance April 02, and she was absolutly wonderful to ride stock for over 28K miles crusing at most 55 mph ( but usually not over 40 to 45 mph).
I've also had the pleasure of ridding and maintaining two other 05 65's owned by a couple of guys from India who live in my town, and they were also a pleasure to ride stock.
Some modifications can be beneficial. My first were Hitchcock's high volume oilpumps, the shift bushing kit from DRS, Classic's blieprinted cluch kit, 18 tooth countershaft sprocket, long header/short muffeler, rejetted carberator, premimum cables, and that made her so sweet to ride.
But I just had to get STUPED, and start making performance modifications on her. Oh yes, I just had to have the head worked over, 9 to 1 compression piston(JUNK), Amal 32mm MK2 carberator(JUNK), and cams.
It's been a total nose bleed, and I regret ever messing with her. The carberator has been a total pain in the butt getting dialed in, and needs constant attention. Timming has been a pain, and luckily Classic came out with a stiffer advance spring whitch helped. Finding gas can be a problem at times, and she WILL NOT run on anything but highest octain available with booster. She gets hot ridding around town because of the high compression, and I live in Bakersfield, California where it get over 100F for months at a time.
She was such a pleasure to ride and own before, and now I dread the thought of having to ride her. Now I'm in the process of saving the money up to put her back to stock, and I can't enjoy her. Leave them alone. Buy a Yamasaki or something bike if you wanna go fast.
Take CARE, be BAD ;-) and ride SAFE...................D.B.