You can retard, or advance, the timing to get your ignition to spark at the correct time to match your engine’s needs and optimise performance. Changing things like the exhaust and carb and fitting a kit etc will mean your timing might need resetting. The factory settings are not always the best even on a new bike. You can reset it by taking off the flywheel, look at the electric’s stator plate and line up the piston to just below top dead centre (you will find the settings in a Haynes manual). The stator plate has slots in the edge where the screws go so you can adjust the timing, if you move it forward (clockwise) you advance the timing (which is the wrong way for you as it makes an engine run hotter and can lead to damage) so you will want to turn the stator plate back (counter clockwise) to retard the ignition and make your engine run colder thus improving reliability and performance. How much you need to alter it depends on the type of modifications you have made and the performance you want to achieve. THIS IS A LOOSE GENERALISATION OF WHAT IS INVOLVED AND IF I HAVE GOT IT WRONG WILL SOMEONE CORRECT ME. If you are not confident doing it yourself take it to a tuner to be set up on a dyno and watch what they do, and note the settings because you could wreck your motor if you get it wrong.