what makes a car release highher than average HC (hydrocarbons) during a smog check?

Answer 1

Either you are running to rich (too much gasoline to burn completely) of a a/f mixture or you are leaking oil into the combustion chamber which would signal bad piston rings. High hc, co count means unburnt fuel. Usually too rich in gasoline
High NOx count means too lean in gasoline or high cyl temps.
C02 and water don't matter

Answer 2

Since you said "HC" and did not say any thing about CO, then Co must be OK>
That would mean that you are LEAN. Not enough fuel to air mixture. This usually means that you have a vacuum leak letting to much air to the measured fuel into the engine.
You did not say what kind of car you have, so can not say if it is Carburetor or some thing else.
I would stay with the vacuum leak for now. Check hoses and intake manifold.

Answer 3

I'll list the most common reasons with a brief explanation:

1. Need an oil change. Fresh oil is not saturated with combustion by-products.

2. Spark plugs. Gap is way off and worn out throwing timing off in some or all cylinders. Cars equipped with original platinum plugs will be listed as lower emission since the platinum acts as a catalyst during combustion making it burn cleaner.

3. Catalytic convertor is out of specifications and needs to be replaced. Most cat. convertors are only good for maybe 100,000 miles unless drivien exclusively in the city where they plug up and fail faster with a shorter life span.

4. A high alcohol contetn fuel or gasoline. Alcohol burns dirtier than pure gasoline. More soot.

Hope this helps.

Good Luck!

Answer 4

hc could be plugs wires air filter cap rotor just tune up should take care of that

Answer 5

bad or worn parts like rings pistons etc, or mixture problems with the carb