There are wet areas around the fuel pipes, there is a strong smell of fuel around the area.
When putting your foot on the accelerator the car does not respond with the same urgency of acceleration. It feels like there is a lag between putting your foot down and the car accelerating, when it does accelerate it feels like a much slower change in speed.
There's a strong smell of fuel coming from the engine bay.
The fuel gauge seems to be going down quicker than usual, the car is using more fuel when driving in the same way as before.
When the engine is running it does sound like it would normally, it can sound like it's struggling to keep running or produce strange noises that sound like it's not running in time with itself.