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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: slammed79 on April 17, 2012, 06:37:22 pm

Title: Failed Emissions
Post by: slammed79 on April 17, 2012, 06:37:22 pm

I took the 74 to emissions today, and it failed the idle test. Any advice on getting the hydrocarbons and carbon monoxide down?

It passed everything else just fine. Could use some help.

Title: Re: Failed Emissions
Post by: bd on April 17, 2012, 07:13:18 pm

What state?  Post the readings.

Title: Re: Failed Emissions
Post by: slammed79 on April 17, 2012, 08:52:33 pm

I'm in Arizona.
At idle it read Hc: 578ppm (400 Max) and 7.02% Co (5% Max)
Under load it read : HC: 43ppm  (400 Max) and 0.18% Co (3.75% Max)

Title: Re: Failed Emissions
Post by: TexasRed on April 17, 2012, 09:41:16 pm

what kind of carburetor?

Also, are you running ported or manifold vacuum for your vacuum advance? If it's manifold, ported may be the better solution.

Title: Re: Failed Emissions
Post by: slammed79 on April 17, 2012, 09:45:01 pm

Quadrajet

Title: Re: Failed Emissions
Post by: 454Man on April 17, 2012, 10:01:32 pm

Mayne try a bottle of that emissions stuff rxp my sister couldn't pass so after about a1/4 of a tank she took out back and passed

Title: Re: Failed Emissions
Post by: bd on April 18, 2012, 12:42:10 am

Make sure you're not dripping fuel from the main nozzles at idle then lean out your idle mixture.  Keep the mixture screws balanced.  When was the last time you changed your oil and filter?  If it's due, change it before you retest.

Title: Re: Failed Emissions
Post by: bake74 on April 18, 2012, 07:37:51 am

     We have a flue gas analyzer at work we use (not on vehicles) but the principle is the same.  It checks and test for CO, Hc, and other things, to get the machinery into specs it is all about adjusting the fuel/air ratio. 
     When was the last time you had a tune up on your truck, and most importanly, have you tried to adjust your carb ?  Especially check what bd mentioned, that will make it run rich for sure.

Title: Re: Failed Emissions
Post by: slammed79 on April 18, 2012, 09:47:51 am

I went back through the log book I keep and found that I'm closer to needing an oil change that thought. Cap, rotor and plugs were done last year. The vacuum advance is on a manifold vacuum port. I'm going to do a tune up this weekend, and run it again. I didn't think it'd been that long, ans since I'm getting 14 or so, I haven't really questioned.it.

Title: Re: Failed Emissions
Post by: VileZambonie on April 18, 2012, 12:53:57 pm

You're running rich by the looks of it. Do all of the tune-up stuff and tell us where your timing is set at both base and advance. Is the engine stock? Are you using a vacuum advance HEI? If so how is it hooked up?

Title: Re: Failed Emissions
Post by: slammed79 on May 16, 2012, 12:22:28 am

I bought a carb off craigslist, rebuilt it, tossed it on and passed with flying colors. There were vacuum leaks at two ports on the carb and it was seeping at the top cover. Also did plugs and wires, and left the timing alone. The cap and rotor are fairly new, so I left them alone as well.

It's nice to be tagged again.

Title: Re: Failed Emissions
Post by: bake74 on May 16, 2012, 05:56:07 am

     Glad to hear you got it legal again.