Some pointers on how you can fix an idle HC and CO smog test failure.

Recently I failed a CA smog test for the first time with high HC and CO at idle. The HC was about 180 PPM (max 150 PPM) and the CO was about 2% (max 1.2%), not too excessive.

Before that I had replaced the head with an LCE street head and mild street cam, LCE header and related components. I did adjust idle mixture to run a bit richer for smoother idle (screw turned out about 6.5 rotations) and I advanced the timing slightly 3-5 degrees I think (for carb 0 degrees is normal).

I figured that the high HC at idle might have been due to idle mixture being too rich, so I set the idle mixture screw back at about 4 turns out. Idles a bit rough when cold, fine otherwise.

I also figured that the high CO might have had somehting to do with a 27 year old CAT and that the old CAT was unable to compensate for high HC. So I replaced the CAT with one from LCE which is just a direct fit magnaflow one, 50 state legal.

Also I used regular gas, I had mid range before for a little while due to advanced timing, though regular works just fine. And regular gas burns cleaner I read, that is, lower octane burns cleaner than higher octane. The reason being that higher octane ignites later and therefore the burn may be less complete. It's a trade off...

After a re-check the emissions were way better, at idle the HC is 2 PPM, avg is 40 PPM and max is 150 PPM, the CO is 0.00% , avg is 0.10 %, max is 1.20 %. I think all changes had an effect, however idle mixture probably helped most to get it passed and a new CAT brought it back down a lot beyond that. I think replacing the CAT would not have been necessary to pass, but at 27 years the old one was on its last legs and looking inside it it had some clogging issues.

I thought it might be helpful for anyone failing smog.

As an aside the smog certificate reports timing to be 0 degrees, either they don't really check, or the amount I advanced falls within the allowed margin (3 degrees +/-?). Or I messed it up a bit and it really is 0 degrees. ;-)

 

smog tips and ca smog coomentary

I agree your carb is still good, running Sea foam can help old carbs. A new cat won't help a gross polluter on mine it made no difference. Three carbs 2 rebuilds and one used, no pass. The state bought my truck. Now I have a rebuild-already passed yrsago.-didin't want to start, cleaned it out, idles for 5 minutes, falls on it's face. Even leaving gas in 6 months, CA eco gas destroyed an echo and stihl chainsawcarbs this year,ruined a Kawasaki concourse of mine by eating pet**** seal caused hydro lock-bent crankshaft. Years a ago many big rig engines were destroyed and replace by bogus CA fuel. I am for clean air but CA is about special interests. The don't count all the environmental damage they ARB cause. Vehicles-Motor homes and others driven under 1,000 a year should not be required.Failing cars based only on Check engine lights and not tailpipe causes lots of low polluting vehicles be diesel hauled,destroyed, run extra hours and miles causing more pollution. Making $1500 pre cats 2002 nissan sentra is non-environmental when a generic in a different mount spot. $200.can do same thing. ARB is out of control-gas tanx of .15-.50 coming to CA Jan1 2015 goes in general fund. Keep your 22rs on the road-no polution has been produced in making these trucks since 1995 or earlier.NONE. Guaranteed Carb's are 179.00,
I am not affiliated-they stand behind theer're work , free shipping, no tax to CA.
Keep the 22rs and re's rolling! Arb =air retard board. Oregon looks awesome.