Topic: BLOWS BLACK SOOT
in Forum: C3 Engines
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Former Member
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deforest, WI - USA
Joined: 12/14/2016
Posts: 13
Vette(s): 1981 work in progress
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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Former Member
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deforest, WI - USA
Joined: 12/14/2016
Posts: 13
Vette(s): 1981 work in progress
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
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
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.
2023 Accelerate Yellow HTC Stingray
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?
Have you scanned for codes since you're getting a CEL?
1973 L-82 4 spd
Former Member
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deforest, WI - USA
Joined: 12/14/2016
Posts: 13
Vette(s): 1981 work in progress
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
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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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
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
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.
Joel Adams
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Overland Park, KS - USA
Joined: 7/9/2003
Posts: 914
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.
2023 Accelerate Yellow HTC Stingray
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.
Q-jets had a foam float that would eventually get soaked and not float which would cause gas to overflow the carb.
1973 L-82 4 spd
Former Member
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deforest, WI - USA
Joined: 12/14/2016
Posts: 13
Vette(s): 1981 work in progress
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
in Forum: C3 Engines
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