I wanted to mention that I'm happy with the performance carburetor sold in the Royal Enfield online store for the Bullet 500. The unit bolts onto the cylinder head, much like the carburetor in the 350 model. This is a much better solution in my opinion than the rubber hose that holds the stock carburetor in the Bullet 500. Especially if one is not using the stock filter, having the carburetor only held by the rubber hose proved quite unstable. Operating the choke tended to push the carburetor down, which sometimes stretched the accelerator cable, which in turn flooded the engine, which ended in much misery. Sometimes the carburetor was coughed out when the engine backfired!
An additional feature is that when one operates the enrichener button, the Bullet becomes a feral rampant beast ready to start just by thinking one will operate the kickstarter. All starts have been on the first kick since I installed it, even in the frigid Louisiana winter, where temperatures reach the 30's sometimes ;-).
A disadvantage is that the enrichener button is on the left side and at least in
my bike this puts it behind the little metal link that holds the engine head, making it a bit inconvenient to reach.
The carburetor has a diameter of 1"7/8 in the rear, so none of the filters sold on the online store seemed to fit. A K&N RC 1290 worked well.