My girlfriend's truck failed the emissions test (aircare) pretty badly. It is an 84 and originally had a 22R, but that died and a 1980 20R was swapped in. The limits for '80 and '84 are nearly identical, so that isn't an issue. The results:

Driving
Max Test
HC 198 223 F
CO 1.82 8.85 F
NOx 2242 121 P

Idle
Max Test
HC 395 1997 F
CO 4.47 7.12 F

Before the test, we replaced the sparkplugs, ignition wires,distributor cap & rotor, fuel pump, vacuum lines. We also rebuilt and installed another 20R carb.

The engine seems to run quite smoothly at both idle and higher rpms. In fact, then engine sounds better than it did before or the old engine before it. Prior to the carb rebuild, black carbon would be spit out of the tailpipe, which i suspect was due to using some oil contaminated gas, but could also have been caused by the carb.

I have setup the emissions to follow what was standard in '80, which is just PCV and EVAP, no Cat or EGR. The vacuum lines are connected very similar to how they should be for an '80.

After it failed the test, we had it diagnosed by a Toyota dealer. They confirmed that it is running quite rich, and suggested going to a smaller primary jet, installing a Cat, and checking for vacuum leaks.

I installed the primary jet from the original carb, which was TINY bit smaller and changed the PCV valve. I played with the idle mixture a bit more and I can get it to idle as low as 600 rpm. The test idle was set at 1000 rpm.

I'm thinking of having a Cat installed, which will reduce the levels somewhat, but the CO will still probably be too high. I think it's interesting that the '84 has a Cat and a few additional emission controls, while the '80 has almost none, and yet the standards are the same. I take this to mean that the truck should pass without a needing a Cat or any emission controls other than PCV and EVAP. It doesn't have EGR and the NOx seems quite low.

The cost limit for a conditional pass is $400, and the diagnostic was $150, so if I pay $250 to have a Cat installed and an exhaust leak from the manifold to the downpipe fixed, we can get a year of insurance.

Does anybody have any ideas what try next to fix it?

 

You need to lean it out. Are you CERTAIN that the choke plate is fully open when you had the truck tested? I would take the air cleaner cover off (while in the lineup) and make SURE that it is fully open and run it through again.

Faster idle speed is better for testing. I'd set it to around 900 rpms and see what happens.

 

I'm certain that the choke plate is fully open - it ALWAYS opens, and the idle goes way up when it closes.

After disconnecting the evap canister, lowering the idle speed, and changing to a slightly smaller jet, we took it through Aircare again.

Driving
Item Max Old New
HC 198 223 206
CO 1.82 8.85 7.41
NOx 2242 121 186

Idle
Item Max Old New
HC 395 1997 1885
CO 4.47 7.12 2.72

The question is, HOW do I lean it out? I don't know how to add more air, so fuel has to be removed somehow. Someone on another forum suggested that the carb was "leaking" fuel into the intake. I've tried to observe the venturis and there doesn't appear to be excess fuel being added, unless maybe it's below the throttle plates and I can't see it. It was also suggested that the truck would keep running with the idle mixture screw all the way in, which it doesn't.

The only possibility that I can come up with at this point is that I did something wrong when I rebuilt the carb.

BTW, does anyone know what that part is that's at the top of the primary barrel, it looks like an upside down U shaped tube? When the engine isn't running and I move the throttle, it spurts out gas. I haven't looked at it when the engine is running.

 

Sounds like your carburetor needs repairs. Possible sticky power valve, etc. Easiest fix would be to get the proper reman carb and drop it on.