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Emissions Results Help

2K views 29 replies 5 participants last post by  KnoxButler 
#1 ·
Hey guys i finally built up the nerve to take my Jeep in to get emissions done...
Background: Bought the jeep (81 CJ7 258 w/ Carter BBD) from a guy who lived in an area that didn't require smog testing, but the jeep did have most of the smog system intact, EGR, etc. however none of it was connected up right. But I removed the exhaust he had on there (cherrybomb) that didn't suit my taste and replaced it with a new cat and muffler. I also did a team rush upgrade and rebuilt the carb using all the settings that came with the kit. I havent done anything with the EGR yet.
Problem: I didnt pass, that was to be expected, but now I need some interpretation and advice as to what I should do next. Here are my results:
Loaded:
HC=47 Standard=220 Pass
CO=0.05 Standard 1.20 Pass

Idle:
HC=372 Standard=220 Fail
CO=4.54 Standard=1.20 Fail

My interpretation of this is that its actually really good. Under load it SAILED by! But while idling its not so hot. When I rebuilt the carb I set the two mixture screws in the front to 5 full turns out from seated. I never took the time to adjust it further than that to lean idle or whatever its called. I bet that would help out at least a little.
Any other advice would be awesome and greatly appreciated!
-Knox
 
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#9 ·
As you mentioned, adjusting your idle mixture screws will help a lot with the idle reading. I would try leaning them out a little (turning them in). 5 turns out is a good starting point for my carb and a lot of other guys with the Carter, but try to adjust to lean best idle and then stay there instead if backing off the recommended 1/4 turn, or just back off 1/8 turn until you pass emissions. The factory setting for the idle mixture screws was closer to 1.5 turns out, but I hit lean best idle well before that coming in from 5 turns. You'll know you're making a difference just in the richness of the exhaust smell as you go. At 5 turns out, the exhaust fumes are probably so rich, it's burning your eyes.
 
#11 ·
As I understand it, even with the BBD, the idle circuit in the carb is in part controlled by the metering screws. Maybe the stepper motor is involved as well and if it's functioning (not sure he's even got a computer on an 81, even the CA BBD's didn't make it onto the scene until 82 if I recall correctly), then at a minimum he should have the idle mixture screws dialed back to 1.5 turns per factory specs.
 
#13 ·
Find a vacuum gauge and set your "best lean idle". You want to hook up the gauge to a manifold vacuum source, start with the mixture screws at 1 turn out, and turn both a quarter turn out at a time. Blip the throttle and read the gauge. the setting that gives you the highest vacuum reading should be the optimal setting.

Google "best lean idle" and you will find a lot better explanation. I set my idle this way, and it burns clean.
 
#14 ·
Ok I was messing around with the mixture screws this morning and I turned them all the way in and started the engine... same manifold vacuum pressure as when they were 5 turns out.
Am i missing something? Could this have something to do with improper step up piston adjustment?

-Knox
 
#15 ·
More to do with either improper low idle setting, or improper metering rod setting.

When idling, the throttle plates should be closed enough so that only the idle circuit it pulling gas though the carb. If your low idle setting has them open too much, the carb will pull gas though the transition circuit.

The metering rods could also need adjusting. The proper method for adjusting them can be found in the FSM. If you bottom out your mixture needles while idling, the engine should me dying, or trying to die.

These two pics are looking at the carb from two different sides, but hopefully you can make sense of them.
 

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#16 ·
Agreed, the engine should die with the idle screws all the way in (be gentle as you bottom them out). Sounds like your throttle plate might be open enough to bypass the idle circuit. What's your RPM at your current idle setting? Is the carb a BBD with the stepper motor on the back or a non-feedback Carter?
 
#17 ·
Ok I figured out that the screws went all the way in, when I got them actual seated the engine did die. Now heres my problem, the tach in my jeep doesnt work at the moment and I want to set the idle screw so that the engine idles at 600-800rpm before I dial in the mixture screws. I dont know how im going to achieve this without buying an expensive tach replacement.
-Knox
 
#20 ·
Yeah, you can set the idle rpm by ear. Tough to describe, but 600 rpm is a getting near a pretty slow rumble (if that term can be applied to a 258!) and 800 will be a smoother higher pitch. If you get it in between, that should be about right, maybe 650-750 rpm. As a point of reference, my well-worn 258 won't idle well below 550rpm at which point it shakes and stumbles, but anything less than 600rpm will sound awfully slow to anyone who's been around cars. The other option is to see if you can borrow/rent a digital timing light with RPM counter or just buy a $50 automotive multimeter with RPM functionality.
 
#23 ·
Knox,
Get a dwell/tach. Not terribly expensive, and you will use it again. If you want I have one, maybe two out in the chaos, called my shop. Let me know if I can help. God bless.
Jon In Tucson
 
#22 ·
They have digital multimeters with RPM count at Advance Auto Parts for around $50 (in-store last time I was there). I would just get it idling in the ballpark by ear and then lean out the idle mixture screws to try to get close to lean best idle. Anything leaner than where you've got it should help with the emissions idle reading. If you're worried that your idle RPM will still be too high (transitioning you out of the idle circuit in the carb), just set RPM's a hair higher than the point where it stumbles and shakes. That should ensure your throttle plate is closed and you're in the idle circuit.
 
#24 ·
Update: So I installed all of the CTO emissions stuff all of my vacuum lines are fresh etc. Adjusted my mixture screws to 2 1/2 turns....

Now my engine runs like crap, the flutter returned and it looses power at the top end... I tried enriching my mixture and that helps a little but thats not going to help my emissions problem.

Im frustrated that I had it running supper smooth all the time and now with all those stupid CTO hoses etc. it runs just as bad as when I first got the car.

Any suggestions of things I might have overlooked?
 
#26 ·
UPDATE: Problem solved, I capped the vacuum advance and adjusted the timing down to 8* (it had been way way high 20+ BTDC) then reconnected the advance to manifold vacuum and it ran great except for the idle being a little lower that it should be (adjusted for emissions).
So set the mixture screws to 2 1/2 turns out from seated. I think im going to do one last check for vacuum leaks and take it in to get tested again tomorrow.

What do you guys thing?
 
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