Just purchased a ZX21 Race motor and want to grind the ports. I would like some advice. I already have a dremel with the grinding stones and polishing pads. I do have an old spare engine to do a test run on. Thanks in advance.

Get diamond bits 3/32 shank and 3/32 cutting end. You will need 2 types cylinder and bulet type. Diamond bits are the best for this kind of work, but pretty expencive, but last forever.
Edward

Thanks for the suggestion. Would you know of any cool site on how to port and polish the ports. Just want to improve flow on the engine. I know grinding the crank will help too but that's for advanced grinders.

I don't personaly believe in ports grinding or polishing and it was proven that it is not changing a thing, but if you look for JP's or other manufacturers web sites you will find there how the modding looks like and can copy it ( any way most of modders do it )
I will sugest you to spend more time on cranck and there is realy power hidden.
Edward

Sweet. Thanks good buddy.