I had an FZ750 i did that to, polished the tank then clear coated it. I used a speed clearcoat. One that is sandable/buffable in 15-25 minutes. Expensive stuff and you have to spray it out of a gun, but it stuck great and still holds up 2 years later now. I've done a few polished aluminum wheels with it too with great success. The trick is making sure the surface is COMPLETELY clean and building up lots of thin coats, letting each coat get tacky before applying another one, despite what the data sheet says for the clear coat. The Martin Senour part numbers for what i've used that both worked great is:
TC732 Extreme Speed Clear and the appropriate reducer and hardener, or
IPC15 Air Bake clear coat and the appropriate reducer and hardener
The IPC15 stuff is amazing, i do lots of bike stuff in it. You can clear a part and put it on the bike 20 minutes later, no fingerprinting, nothing. Not brittle at all either, i've done some sport bike plastics with it and you can bend the crap out of it no worries of cracking or flaking.