High hydrocarbons! Please help!

[brsslam]

Okay i have a 1986 Chevy k10 with a 350 in it. i took it to get the emissions done and I failed on the HC during idle. I was 103 over. But I passed on the high speed test. what can i do to bring it down? My truck has a 350 with a edelbrock 4 barrel carb on it and a MSD ignition system. thanks in advance! If there is any thing else you need please ask.

 

[skysurfer]

The most likely causes are vacuum leaks and/or a burned out catalytic converter. If it's never been replaced I would suspect the cat, mine was a hollow shell after 15 years and 130K miles. Replacing it with a new aftermarket unit cut the HC and CO readings by more than 50%.

 

[chengny]

High HC levels = unburned fuel in the exhaust gas stream = incomplete combustion.

Incomplete combustion is due to engine misfire - as a result of (in order of most to least common):

1. A weak or non-existent spark in one or more cylinders (coil, cap, rotor, wires, plugs, etc)

2. Excessively lean A/F ratio (either by intake manifold vacuum leaks or improperly adjusted carburetor)

3. Leaking exhaust valve(s) - (allows raw fuel to be blown right into the exhaust piping on the compression stroke)

4. Improper (usually over-advanced) ignition timing

5. Poor compression (normal reasons like rings/valves)

6. Overly rich A/F ratio (just too much fuel to allow for a complete burn-off)

So basically, excess HC levels are a good indicator that your engine is not operating at it's best. Start off checking/repairing the easiest/cheapest stuff first.

 

[79K10]

i had a 305 running a holley double pumper on an eddy performer intake,mild summit cam, headers 2.25 pipes into flows ... guy at the smog shop said i was pushing 3000 hc ...hahahaha... thing ran like a nascar ! merica!

 

[87ChevyR10]

Move to a state that doesn't check emissions. IE, Kansas.

 

[89Suburban]

Lean the idle mixture down. Sometimes they will intentionally create a vacuum leak to get it to pass by pulling a vacuum line off something. New cat won't hurt either. I passed PA's strict sniffer with a $30 universal cat from Rock Auto.