APE makes adjustable cam sprocket for all the popular bikes, Yamaha, Suzuki, Honda and Kawasaki and probably some others that I'm not aware of..
Degreeing the cam in, is probably one of the most overlooked performance modifications! For very little money and a couple hours of work you can make some serious horsepower changes to your stock engine.
Oh and Snakebite I'm pretty sure the intake valves close before BDC. I think almost all engines have the intake valves close before BDC.. every valve opens or closes just before/after top or bottom dead center.. I think my car is like 12 or 16 degrees from center if I remeber correctly. It's not like they're dead on the money BDC and retarding the timing slightly would put them on the wrong side of the crank rotation. It will be moving it in the wrong direction for making power and being efficient though.
Depending on what year you have the Intake Valve Closes either 52* or 60* After Bottom Dead Center. Almost all cams are timed that way.
There is a posting of cam specs in the page before this one Titled 750/650 Cams.
