Assuming you are referring to a small 2 stroke engine, the most common way to start a flooded engine is by pedaling the bike or using a kick start. If the engine is completely flooded, it will not start no matter what you do. To fix a flooded engine, follow these steps:
1) Remove the spark plug and look at it to see if it’s wet. If it’s wet, then proceed to step 2. If it’s dry, then your problem might be with the spark plug itself or with the ignition system. Try replacing the spark plug and/or checking the ignition system before proceeding to step 2.
2) Pedal the bike or use a kick start to get the engine turning over. As it’s turning over, keep an eye on the spark plug hole. You should see fuel squirting out of the hole as long as the engine is getting enough gas.
3) Once fuel starts squirting out of the spark plug hole, quickly screw in a new spark plug and tighten it down. This will stop fuel from entering