Hi, i got a 78 camaro with a 350 in it. It has high hydrocarbons on an efficiency test. One of the cylinders makes a slight knocking sound untill I warm up the car, is this a weak lifter? It can also take a while to startup if it has been sitting a while. I got all the spark plugs and wires changed, sounds slightly better but not a significant difference. I have not had the car long, it was in storage for many years before I got it. Any suggestions on what I should look at next is appreciated.

 

Try a compression test.

 

is the timing right? Hydro carbons are from unburned fuel going out the exhaust, id say lean the carb and check the timing, should clean it up

 

does that year have a cat converter? my 92 had the same problem passing emmisions. you could try driving it around getting the cat real hot and then getting directly in for a test. when it sits waiting in line, it cools off and causes a high HC count.

i put in a new CC and passed with all zeros

 

That would have a cat but they never go bad. They are really big and I've never seen one go bad in those cars

 

I would do a manual compression test to the engine. If the noise is a knocking noise and goes away when it warms up, I would say thats a piston knock. Are you hearing the noise from the top or the bottom of the motor? A lifter would make a ticking sound and would usually get louder as the engine warms up if its not pumping up. Hard start and high hydrocarbons could mean that the carb could need rebuilding or adjusted if the car has been sitting for a long time.