Why there is a small lag before the engine starts?

This is due to the engine's oil system. The oil needs to circulate through the engine to lubricate it when you start the engine. This can take a few seconds, which is why there is a small lag before the engine starts. You can solve this by starting the engine and letting it idle for a few seconds to give the oil time to circulate. You can also try starting the engine with the throttle slightly open to help the oil circulate faster. If this doesn't work, it's best to consult a professional mechanic to diagnose and solve the problem.