The "tik-tik" sound you hear after switching off the engine of a bike with a petrol engine, especially after a long run, is typically caused by the phenomenon known as engine pinging or engine knocking.
Engine pinging occurs when the air-fuel mixture in the combustion chamber ignites prematurely or unevenly. This can happen due to a few reasons:
Heat and Pressure: After a long run, the engine components, including the combustion chamber, become very hot. When you switch off the engine, the residual heat can cause the air-fuel mixture to ignite spontaneously due to the high temperature and pressure inside the chamber.
Carbon Deposits: Over time, carbon deposits can accumulate on the spark plug or within the combustion chamber. These deposits can become hot spots that can ignite the fuel prematurely, leading to the "tik-tik" sound.
Low-Octane Fuel: Using low-octane fuel can contribute to engine pinging. Lower-octane fuels have a lower resistance to premature ignition, so when used in high-performance engines or engines with high compression ratios, they are more prone to pinging.
Timing Issues: If the ignition timing is too advanced, it can cause the fuel to ignite before the piston reaches the top of its compression stroke, leading to pinging.
It's worth noting that some level of ticking or clicking noise can be normal as the engine cools down and metal components contract. However, if the sound is excessive or persistent, it's recommended to have the bike inspected by a qualified mechanic. They can check for any potential issues, such as carbon buildup, fuel quality, or ignition timing, and make necessary adjustments or repairs to address the problem.