Topic: Another smog question???

[krash81]

So I just tried to get my truck(79) passed the smog test..FAILED. Everything was good except my CO%. After reading through all the threads about smog testing I see that it's running too rich. My question is since the truck is from Los Angeles and I'm the first person to register it in Utah, maybe the jetting wrong for the higher altitude??? I've already done all the tune up, oil change, valve adjustment stuff. And am going to rebuild the carb before i try the test again. Should i change the jetting while it's apart??  

[*ROKTOY*]

If you can get a leaner main jet, I would.

[tech201]

If you decide to re jet don't go overboard if you run it lean it will raise the hc got to find that happy medium.

[krash81 [OP]]

But would the jetting be different from california and utah trucks from the factory? If not then I should be able to get it to pass like it is??

[emsvitil]

What's your altitude?

I believe there was an high-altitude calibration, but don't know what altitude it started at.

[krash81 [OP]]

Salt Lake is 4,220 ft.

[emsvitil]

http://www.asashop.org/autoinc/oct2001/techtotech.htm

[krash81 [OP]]

Good article...and food for thought.

[jimbo74]

you need to make sure you have the HAC system... some cars didnt have it.... im surprised that the restrictions where you are are being mroe strict on you than what it had in CA --- and everyone here says its the harshest state...... coming from LA i am surprised again, as that is a dyno smog area

[krash81 [OP]]

Thats why I was wondering aboout the jetting. Since the air is thinner up here. It measured 6.55 co% and max is 3.14 at 25 mph. The guy was way cool. He ran it on the dyno twice at no charge. He told me to rebuild the carb and come back. Anyways I just took the top off and there's alot of debris in the float bowl. So I'll run down to Napa and get a kit. Hopefuly that does the trick. Plus a P/O did a number on some of the vacuum hoses for some reason unknown. But I'm sure alot of you know how that is..

[Plekto]

Yeah - CA's limits are like half that.  Carbs need work, for sure.  Oh - if you can advance the timing a couple of degrees and still pass, this might help. (don't know how far you can get away with though on their test)   Basically you'll be leaning it out.   

Oh - and those messed up vacuum hoses - probably not helping any...(probably has a plugged or nearly dead EGR valve - check that)

[1stgenboy]

Thats why I was wondering aboout the jetting. Since the air is thinner up here. It measured 6.55 co% and max is 3.14 at 25 mph. The guy was way cool. He ran it on the dyno twice at no charge. He told me to rebuild the carb and come back. Anyways I just took the top off and there's alot of debris in the float bowl. So I'll run down to Napa and get a kit. Hopefuly that does the trick. Plus a P/O did a number on some of the vacuum hoses for some reason unknown. But I'm sure alot of you know how that is..

co is partially burnt fuel.  If I had a truck that age and the cat was old or original I would spend the money for a new highflow cat.  That will clean up the 3+ points you are off easily and improve milage and power.

[jimbo74]

i was told that you should be retarding the timing to make it run not as rich

[Plekto]

Well, it's tricky...  If you have a higher flow carb or cat or exhaust than stock, you need to make it run a bit hotter to burn more of the fuel.  My timing was at +5 degrees and I set it back for the test.  Sometimes an older engine also needs slightly advanced timing as well as compression starts to get lower.  There are two factors - how lean or rich it is and how efficiently it is running.

+5 degrees - 19mpg avg(noticeable boost in city mpg)
CO 0.09/0.71
HC 43/58
10% higher NOx.  Slightly higher power felt as well - probably 5hp.

+0 degrees - 17mpg
CO 0.18/0.33 - efficiency of the combustion.  Good for smog.
HC 71/48 - this is unburnt fuel.  Bad for mpg.

Net effect was that the higher speed emissions were better at the expense of slower driving emissions with it stock - due to bumping the compression a bit.  Though it tended to also ping a bit, needing a bit of fuel additive or midrange fuel.

[krash81 [OP]]

After a week I'm still waiting for my carb kit from Napa..hmm. Don't know where they get the good reputation from. They seem to disappoint me alot lately..
Anyways..my cat looks fairly new. Not too much corrosion. And I had a built chevy 350 with no cats or smog pump, egr emissions crap pass easily before. I figured if the chev did, I might be able to get the yota to do the same... I don't know. Im still learning about carburetors, so this is a good learning experience.lol

[krash81 [OP]]

Woohoo!! got it to pass. i rebuilt the carb and went one size smaller on the primary jet. But i think I'm switching to a weber cause the stock runs like . ha. at least it passed

[Twisted Minis]

Yeah I just ran smog here, we are only allowed 1.64 CO.

I had to rebuild my carb as it was running too rich. And I got him to run it in 3rd gear for the 25 MPH test and it passed that.

[dt]

octane booster does help,my friend just smogged his 1981,...rebuilt carb...new cat and he passed