My brother is a tech in Sacramento. He is a test only shop. How many times have you worked on an engine trying to figure out a problem, and been wrong, only to find out it was something else after buying parts? Dead battery so you buy a new 1 only to find out that the alt was dead, or the regulator or the plug. There not there to fix your car, but to give you ideas. In fact, they are not really supposed to give you advise just for this reason. Ill give my brother a buzz real quick and see what he says to try, but he has always said that even some of the worst cars can pass with just a new cat. Only the cat may last 100 miles before dying due to problems that are causing the car to not pass to begin with.

try to fix it first.. but if you run it to about 1/4 tank and add 1-2 gal of methanol to the tank it will clean it up a bit, a lot a bit.. if you ad meth and its really runs bad add a tad more gas.. then after smog test fill er up

not really, ur only adding a lil bit.. done it many times before on carb engines.. u are only adding a gal or so mayb less then your fillng it up after u test.. but also like i said fix it first.. then as a last resort do the meth trick.. i know in some states you dont pass the smog u cant drive it then no ride to work.. so if all else fails use the meth... actully 1/2 gall will clean it up pretty good.. did this on my 74 van many yrs ago.. had carb issues.. no money and no job. had to do what i had to do..van is still runing same fuel system, no problems.. i did fix the carb tho, same fuel lines.. my local NAPA gave me this trick and the meth

As you troubleshoot it..
Find a friendly smog guy who will do a pretest..
If you keep going back and failing the car will be assigned as a Gross Polluter..

Just my $0.02..

Move to a normal state. The truck is 34 years old .

Yeah... THAT was helpful.

The truck is equipped with the FEDERAL emissions package. No catalytic converters, no smog pump, EGR or thermostatic air cleaner. Pretty basic stuff.
I like the idea of running the additives and cranking up the idle some. Thanks for the suggestions!

The Trail Duster JUST passed the smog test!
I think that after the 2nd test, it became clear that it may have had excessive idle HC numbers because the engine wasn't as warm as it was during the first test.

Test#1:

1:11 PM
Idle rpm 674
HC PPM 300 MAX
HC PPM 651 measured

2500 2585
HC PPM 350 MAX
HC PPM 36 measured

Test #2
9:20 AM
Idle RPM 862
HC PPM 300 MAX
HC PPM 1003 measured

The differences between the two tests? I replaced 2 vacuum lines, checked for leaks, replaced the carb base gasket, removed a vac line to the inop cruise control and raised the idle speed, PLUS the engine was a little cooler.
Yesterday I talked with the tech again and he suggested trying another carburetor or new plug wires. At home I DID replace the cap, rotor, plug wires AND add 1 1/2 gallons on E85. I raised the idle and backed out the idle mixture screws 1/2 turn. here are the numbers:

Idle 974
HC PPM 300 MAX,
HC PPM 28 measured !!
2500
HC PPM 350 MAX
HC PPM 49 measured!
FANTASTIC! As always though, I'm curious as to what made the difference. I remember the guideline : "Do only one change at a time."
In this case, I had to play it safe. I was lucky to find a NO PASS, NO PAY smog shop nearby. I suppose that I'll just keep a record of what I did for the next time. Thanks for the suggestions, Greg

Post the CO numbers too. Sounds like it had a lean miss due to the idle mix screws being too far in, but without those numbers it's just a guess.

Thanks... here we go:

Test # 1
CO %
Idle 674 rpm
3.00 MAX, .24 measured
2500 2585
3.50 MAX, .07 measured

Test # 2
CO %
Idle 862 rpm
3.00 Max, .16 measured
2500 2478
3.50 MAX, .05 measured

Test # 3
Idle 974 rpm
3.00 MAX, .55 measured
2500 2535
3.50 MAX, .08 measured

It runs smoother now than before. I'll probably lower the idle a little though. No dieseling on shutoff.

I'm not a smog expert, BUT it is clear that when you raised the idle you went sufficiently off the idle circuit and into the cruise circuit, indicating that the problem is in the carb idle circuit and one of the big reasons that I sold my '79 late last year and replaced it with the Durango (let the computer adjust things properly - or at least better than I can). Nothing against carburetors, just against carbs that have to pass smog....and not a judgement on you for having that truck, just what works for me.

When I lived in Sac and had to smog my 79 trailduster, I had a heck of a time with the original worn-out carb. I bushed the shafts, kitted it a dozen times, and still had to cross my fingers with it. I also had to replace my warped/cracked fuel bowl with several junkyard parts that were also warped over the years.

I finally bought a holley spreadbore smog legal carb and I got fantastic driveability and power (compared to the old carb) and never worried about passing smog again. Just an option for next time.

Greg, what smog shop did you go to? I'll be looking at doing this next year. If it's close to you, that's fine. It'll give the truck a good long time/drive to heat up and be ready for the test. But mine's just a 360 2BBL.

I went to "Tailpipes" on Greenback lane in Orangevale. I know of another No pass-No pay place on North Antelope in Roseville.
My truck with full time 4wd had to be tested off of the dynomometer. PLUS, I have Federal emissions. Far fewer things to go wrong.

Congrats on the pass. Reminds me of the few years in the 80s that I had to hassle with getting the RR smogged when I lived in the Bay Area. Got the carb worked on, different air cleaner, aftermarket NOx kit (CA car originally), yada yada. What a goat rope! Finally got tired of doing it and just registered at my sister's house in Bend, OR to avoid the test altogether. Not worth it for a car that was driven MAYBE 1000 miles/year...