Why when you press on the gas pedal in accelerates but then slows down?

When you press the gas pedal, you are opening a valve that allows more fuel to flow into the engine. This causes the engine to speed up. However, if the engine is not getting enough air, the fuel will not burn properly and the engine will slow down. This is why it is important to make sure that your air filter is clean and that your exhaust system is not blocked.