BS4 Royal Enfield Classic 350 stops all of a sudden as not enough fuel is coming out in On position. Even changed the petcock and cleaned the tank

If the issue is insufficient fuel flow*, these two possibilities also suggest themselves:

a) There is frequently a fine-wire screen inside the tank, or inside the petcock, to prevent dirt and grit from passing through the petcock and thence to the carburetor. Drain the tank, remove the petcock, and inspect carefully. If such a screen or filter is present, clean or replace it.

b) The fuel line between the petcock and the carburetor may be internally blocked or partially blocked. I would replace the line to ensure that it is completely open.

• Your statement "Bike stops suddenly..." does not indicate insufficient fuel flow. If insufficient flow is the problem, the motor will sputter and lose power, taking seconds or even minutes to go from running to not running. If the motor actually stops running suddenly - as though you had turned the kill switch or ignition off - then the bike has an electrical problem, not a fuel flow problem.