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Topic: BLOWS BLACK SOOT

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BLOWS BLACK SOOT (1/18)
12/15/16 6:32pm

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

I HAVE A 81 THAT IVE OWNED FOR 2 YEARS ITS NEVER RUN RIGHT EXCEPT WHEN I TOOK FOR MY FIRST TEST DRIVE I HAD A REBUILT Q -JET INSTALLED IT HELPED WITH THE STALLING BUT SHE STILL BLOWS BLACK SOOT OUT THE EXSHAUST,IDILS REAL ROUGH ,5-7 MPG'S ,SMELLS OF GAS , CHECK ENGINE LIGHT COMES ON AND OFF IT ALL SOUNDS LIKE ITS RUNNING RICH BUT DOESNT THE CPU CONTROL THE MIXTURES, I"VE REPAIRED ALL VACCUME LEAKS WHICH REALLY DIDNT CHANGE MUCH EXCEPT LOWERING THE RPMS AND LOSING MY FAST IDILS WHEN COLD AT START UP DOES ANYONE HAVE A SUGGESTION???????

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Re: BLOWS BLACK SOOT (2/18)
12/16/16 8:07am

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, - Canada

Vette(s):
1975 L48 Stingray 1992 LT1

Joined: 12/24/2013
Posts: 414

sounds like a fuel mix problem, always eliminate the little things first, like filters,sensors etc. Hopefully you don't have to dig much farther

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Re: BLOWS BLACK SOOT (3/18)
12/16/16 2:13pm

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

I have changed both fuel filters, which sensors should I replace or is there a way to check each sensor also replaced air filter, plugs, so far nothing has help, this cant be (hopefully) the only 81 that have these issues

Re: BLOWS BLACK SOOT (4/18)
2/16/17 8:16am

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, - Canada

Vette(s):
1975 L48 Stingray 1992 LT1

Joined: 12/24/2013
Posts: 414

|UPDATED|2/16/2017 5:16:14 AM (AZT)|/UPDATED|

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Re: BLOWS BLACK SOOT (5/18)
12/16/16 9:53pm

73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 866

Does the car still have the cat? O2 sensors would be a good place to start.

Have you scanned for codes since you're getting a CEL?

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1973 L-82 4 spd

Re: BLOWS BLACK SOOT (6/18)
12/17/16 11:03am

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

yes it still has the cat, and 02 sensor which I was thinking to remove and leave it plug in and tie wrap it out of the way do you think that would be a good test, I'm not really sure that the last shop I took her too really replaced the carb, its a long story but the more I dig into her the more I don't trust anything they have done. The black soot is the big question it happens in all temperatures has no smell and blows wet until completely warmed up. if it was a problem with the valves won't I get a lot of smoke out of the breather port on the valve cover

THANKS FOR ANY INPUT ANYONE HAS

Re: BLOWS BLACK SOOT (7/18)
12/18/16 9:37am

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, - Canada

Vette(s):
1975 L48 Stingray 1992 LT1

Joined: 12/24/2013
Posts: 414

It doesn't necessarily have to be the valves, it could be on a piston, another tell tell story would be to read your spark plugs they will tell you a lot without getting to technical, always always checkt the simplest things first ,sensors plugs, etc hopefully you don't have to go to far and it is not anything serious

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Re: BLOWS BLACK SOOT (8/18)
12/18/16 11:29am

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20128

Black soot is a FUEL problem.....the engine is getting more fuel than it can burn. You have a carb issue, regardless of what "they" told you they did, your carb is the issue. Either the choke blade is stuck, or not being pulled off by the pull-off valve, the choke adjustment is way off, or the float level is way too high/float stuck. Fix the carb issue first. Thumbs Up

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Re: BLOWS BLACK SOOT (9/18)
12/18/16 12:55pm

73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 866

A couple of ways to tell if they replaced the carb is does the "new" carb look new and how much they charged. IIRC, the 81s had the computer controlled Q-jets which added another layer of complexity.

Q-jets had a foam float that would eventually get soaked and not float which would cause gas to overflow the carb.

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1973 L-82 4 spd

Re: BLOWS BLACK SOOT/please help (10/18)
12/18/16 7:55pm

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

Thanks for all the input it really is appreciate

Okay ill pull the plugs and see what they look like

I sent her into the shop that I had been using in fl before moving north to the FROZEN tundra (don't ask) she would stall on the slightest incline I left her behind and trusted that he would fix all the issues he called said it was running like new ,paid the bill and had it shipped to me the carb look new and clean but the only thing that look strange was the pitting on top of the secondary flapper it look just like the pitting on my original and after not receiving any paper work and being told that it was a new rebuilt replacement any way its left me with a bad taste in my wallet about taking her to a new shop. she also still has a slight pop and hesitation, and getting back to the bigger question doesn't the cpu control all the fuel mixtures on the 81 or just some or very little it looks all original except no smog pump , headers ,and upgraded radiator. Does anyone have any advise on how to check if the carb is actually the same or a replacement thank you for all your time,

Merry christmas

Re: BLOWS BLACK SOOT (11/18)
12/18/16 7:58pm

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20128

ECM only controls the idle fuel mixture and the ignition timing....nothing else. I would suggest getting the codes, and see what the ECM has for info on the problem. It is definitely a carb problem. Perhaps it was running fine when it left Fla., but bouncing on a transport could have caused a problem.

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C3VR Lifetime Member #56
My Link

(click for Texas-sized view!) NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Re: BLOWS BLACK SOOT (12/18)
12/19/16 10:18pm

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

I pulled the #8 & # 6 plugs today and they had the same soot as I'm blowing out the exhaust so I'm really hating to think that the carb was not replaced but fixed to stop it from stalling so more questions do I try and find another shop or send it to a rebuilt facility which all they do is rebuild Q-jets all day or buy a new one or replace it with a bigger and better compatible one don't want to reinvent the wheel I want a plug and play any ideas

Re: BLOWS BLACK SOOT (13/18)
12/20/16 1:42am

73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 866

Get a Q-jet repair kit and rebuild it yourself. If they truly didn't give you a new carb, then I would get a new float also. You don't need a bigger carb. IIRC, the Q-jet is good to at least 700 CFM.

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1973 L-82 4 spd

Re: BLOWS BLACK SOOT (14/18)
12/20/16 5:45pm

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Flanders, NJ - USA

Vette(s):
1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

Joined: 1/27/2004
Posts: 2552

You said you were going to get rid of the O2 sensor? Can't do that if you keep the 81 carb. The computer needs it.

That black smoke is a fuel issue for sure, way too rich.

Hope you get it sorted out.

Dave

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Dave's '82

Re: BLOWS BLACK SOOT (15/18)
12/20/16 6:44pm

manchestershark

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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 2387

Take a GOOD look at the choke. Also, if you can get your hands on the MARCH 2017 issue of VETTE magazine, there is a good article on rebuilding a Q-jet. The cross shafts may need drilling and rebushed. A VERY noted problem after years of wear. It could be sucking air past the shafts and creating a different mixture.

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Re: BLOWS BLACK SOOT (16/18)
12/28/16 9:01pm

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

I cant find out how to lean out the carb only info on the net was only about the choke any ideas

Re: BLOWS BLACK SOOT (17/18)
2/16/17 12:28am

sPearson66/81
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deforest, WI - USA

Vette(s):
1981 work in progress

Joined: 12/14/2016
Posts: 13

OKAY IT WAS THE Q JET THE HOLE TIME IT WAS NEVER REPLACED I THINK THE SHOP JUST SPRAYED SOME CARB CLEANER AND BILLED ME ANYWAY AFTER READING ANYTHING I COULD GET MY HANDS ON THESE 4EME ARE PRETTY SIMPLE TO TUNE BUT THE EASY THING WAS TO JUST UNPLUG M/S AND THE TPS AND SHE RAN GREAT FOR THE FIRST TIME SO THERE WAS THE PROBLEM THE DWELL WAS OUT AND THE VOLTAGE TO TPS WAS WAY HIGH ALSO SET TIMING TO 12 BDC AND 36 ADVANCED VACUUM IS STEADY AT 18 FINALLY NO MORE SOOT NO MORE BLIDING SMOKE

Re: BLOWS BLACK SOOT (18/18)
2/17/17 8:46am

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Flanders, NJ - USA

Vette(s):
1982 Black, ZZ4, Hooker Side Pipes, 3.55 Rear, Rebuilt & upgraded 700R4, All new suspension, brakes, & new Charcoal interior.

Joined: 1/27/2004
Posts: 2552

Glad you finally got the issue resolved. Have fun!

Dave

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Lifetime Member #116
Dave's '82

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