Thats a science question without more details. Usually, hydrocarbons is the unburned fuel that comes out the tail pipe. So the closer to 100% of the fuel gets burned, the better. If your car is not passing a test, there are several possible causes, including a faulty thermostat or catalytic converter.
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Thats a science question without more details.
Usually, hydrocarbons is the unburned fuel that comes out the tail pipe. So the closer to 100% of the fuel gets burned, the better. If your car is not passing a test, there are several possible causes, including a faulty thermostat or catalytic converter.