A lot of you know I have been working on my "rich" condition off and on with my 77 280. California has some tough smog laws! So after replacing, rebuilding, testing, cleaning, adjusting, rewiring, searching, trial and error, cursing (lots) she passed. I'm actually looking at the numbers now and have come to the conclusion that I can richen her up a little. The CO and HC readings are very low, too low for the engines sake as far as the CO goes. The smog tech said he has never seen numbers like these on a Z. So that made me feel pretty good. Thought you all would like to know. And thanks to those that offered help and ideas during the past 6 months.

Edited May 19, 201212 yr by rcb280z

Very cool! I sure am glad I do not need to smog my 77 here in Seattle, but if I did it would make me tune up my car more often. Good job.

That is fantastic! So now that you have tasted victory, perhaps you could list the steps you took to remedy the issue. I am betting there are a bunch of others out there with similar problems. I know I am interested - even though I am in Texas I still would like to have my Z running as clean as possible.

Congratulations again

Congrats! Maybe drive it for a little bit and then pull the plugs to make sure that your aren't too lean?

Yeah Capt. Obvious, just what I am going to do. After I make a small adjustment to the AFM....to richen just a little. I can tell I am a little lean...the test results prove it also. Andrew, this was definitely a challenge. And one I thought I wouldn't win a few months ago. It was just a matter of understanding what the service manual was saying and I needed you all for that help a few times. Andrew, I will share everything I learned whenever you need it. I'm on this site daily.

Hey Grantf, YES be very thankful you don't need to smog! Unless you have owned your Z from day one and have performed the maintenance required and didn't have a PO get in there and screw things up then it can be tough. Anyway, now I can install my aluminum radiator and start other projects on my Z. Will post that as well.

If the HC is low it is not too lean. When it gets too lean the HC will rise even though the CO continues to drop. Keep in mind the smog test is done at idle and light throttle. It can be a bit lean at idle and rich at large throttle openings and still pass the test.

Actually the smog tests are done on dyno's now in CA. 15 mph and 25 mph tests. I believe they no longer do idle tests. I got to watch the process. The tech walked around to the back of the Z and shook his head. I asked if something was wrong and he said "oh no, thought the probe came out of the exhaust because the numbers are so low"! I'm not so concerned about the HC. CO is 0.01 at 15 mph test and 0.00 at 25 mph test....too lean depending on who you talk to. You are allowed 0.50 CO. HC readings were up there (but still really low for CA standards)) for both 15 and 25 mph test. It's only going to take a very small adjustment of the AFM bypass screw to dial it in where I want it. Just looked at plugs and they show lean as well. The leaner you go the more HC you produce. I am going to a shop here in Ventura to have them test it after I do a small adjustment and will post results. I'm curious just how much the numbers are going to change after my small adjustment.

Congrats!!

Wow, I sure am glad we don't have smog testing here in VA, not that my exhaust would be that awful. It sure must be a PITA!

Curious: I think I have my AFM dialed in just about right, but I think I am running a little lean. So what is the difference between enriching the mixture through AFM adjustment and installing a resistor in line with the WTS that some have done?

Never did the resister inline so I'm not really sure of the difference other than being able to do it while you are in the drivers seat while driving. I'm getting between 22 and 25 mpg right now and my plugs look good. She runs very well.

I don't know how sensitive the idle mixture adjustment screw is. I also don't know how much throttle opening you needed to maintain that 15 and 25 mph on the dyno, but remember that since the bypass screw is in parallel with the throttle butterfly plate, it will have more impact the less the butterfly is open. In other words, if you close that screw down some, it will make you richer across the entire operating range, but the change towards richer will be greater at idle than at WOT.

I'd be interested in hearing how much of an effect that screw has for say one turn or so.

Ok here we are. The HC dropped slightly when we adjusted the bypass screw in the AFM richer "CW". 1 full turn took CO from 0.01 to 0.28 still way within spec. This was the 15 mph dyno run. Took it out for a spin and am very happy with how she is running. I can't remember what the 25 mph dyno numbers were but they only increased slightly as well. Going to run it around a couple more times and then check plugs. If they look good I'm going to stop with adjustments. She is running fantastic!