Having a high HC (hydrocarbon) is a sign of poor fuel ignition. Beyond just the engine's ignition system being responsible for that problem, there are a number of reasons for high HC.
With engine ignition timing measured in degrees before or after Top Dead Center (TDC), ignition timing failure could happen with the timing set to a degree that varies from the general requirement. For example, setting it at 15 degrees rather than 10 degrees could trigger such a failure.
The engine will produce high HC if any of the vehicle's ignition components---ignition coils and wires, distributor and spark plugs---are defective.
The vehicle should not have any condition that will cause unmetered air to enter the intake manifold, and then the combustion chambers. This includes vacuum and gasket leaks.
The vehicle should have a catalytic converter (CAT)---a key component for the combustion process---that functions properly. Otherwise, it can trigger high HC.
There should be no defective smog pump and related emissions system components, since high HC can be caused with the reduction of oxygen needed to burn out remaining fuel in the exhaust.
One of the rarer causes of high HC, low cylinder compression is caused by one or more of the car's cylinders having defects with intake or exhaust valves, piston rings or burned head gaskets.
