Mark A Shields

OK, I just recently started trying to readjust my A/F screws, my car is running rich, I have black powder around the tailpipes and horrible mpg. I won't be able to have it rejetted for a couple of weeks. But here's the deal I only have to pass an idle test for emissions. I have been 4 times and my readings have been the following before adjusting the A/F screws
Hydrocarbons 880ppm limit 220
CO 7.4pct limit 1.2pct
CO2 6.8pct limit 6.0pct
Now after adjusting the screws
my HC is down to 581
CO down to 4.0
but my CO2 is up to 10.49
I am guessing adjusting the screws helped but why did the CO2 jump up.
Please help.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Exhaust
"There is nothing more addicting than speed"

five7kid

iTrader: (14)

What's your timing set at? Are you using ported or manifold vacuum for the vacuum advance? Initial timing should be at around 10, use ported vacuum. Did you have to adjust your idle speed after adjusting the mixture screws? That may explain the CO2 jump.

After you've checked those things, put on a cat. You'll pass with flying colors.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam and intake, World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Edelbrock 1901 Q-Jet, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

Mark A Shields

Well I would rather not put on a cat, doesn't that hurt performance. No I didn't have to readjust the idle speed, it's manifold vacuum I believe. But am I heading in the right direction though by adjusting the screws?

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Exhaust
"There is nothing more addicting than speed"

Mark A Shields

I'm not sure what the timing is set at, my brother did it, and I know he advanced it.

------------------
'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Exhaust
"There is nothing more addicting than speed"