To expand on Avistar 23's reply, If you flood these engines with too much fuel and it gets into the cylinder, you get what is called hydrolock. That is, there is lots of fluid in the cylinder instead of air and the fluid won't compress and locks up the engine. Don't try to turn it on through by hand or with a powerful starter as you can easily bend the connecting rod. Hold the engine with the exhaust outlet down and then work the crankshaft back and forth until the fluid pours out of the exhaust and then carefully turn it on through by hand and clear out the excess fluid.

This can easily be caused by pumping fuel into your tank with the vent line still connected to the exhaust. Depending on the position of the engine, the excess fuel will maybe flow directly into the cylinder on top of the piston and there you have hydrolock. You should always remove that vent line from the muffler before you fill your tank and run it into a catch bottle to catch the overflow. Saves the pit area pavement surface and also costs you less money by saving the fuel that would be wasted. You will get at least one extra flight out of a gallon of fuel.

Welcome to the sport. There are lots of these little things to learn and in a year you will be helping others.

Coop