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I would like to ask for help and advice on overhauling the fuel system on my C3.
I am the proud and motivated owner a 1970 C3 with a 454 big block engine (LS5) and an automatic transmission. This car was a barn find and hadn’t moved in over 15 years; she was stored in a garage but was never prepped for storage, languishing away with all her fluids (including gas) still inside, with only spiders for company.
The Corvette was ordered in Feb 1970 and produced and delivered in March 1970. The original order paperwork indicates a 390-HP 454 cu. in. engine, large 4 bbl. carb, hydraulic lifters & high-lift cam and a Turbo Hydra-matic transmission. The carburetor is a Rochester Quadrajet, stamped 7029200 (replaced at least once in 1981, according to my decipherment of the receipt logs I got with the car, but the stamp indicates this one was made for Chevrolet in 1969 according to federal standards, so it could be the original still).
The gas cap has the word “vented” stamped on it, and the charcoal canister does not exist - this was just before the emissions regulations, and was purchased on the East Coast, far away from California laws. Interestingly, I did discover that the fuel pump is an electrical one: a Carter P4070, if I am not mistaken, although I can’t exactly tell without dismounting it.
The gas had long since turned to turpentine; I pumped out manually whatever I could through the gas cap opening (almost exactly 5 gal), making my entire garage smell like brain damage, and I’ve removed the spare tire and spare tire carrier.
My goal is to make this car as safe and clean as possible, without converting to EFI. My plan currently is to:
Drop the tank and clean it
Flush the fuel lines with ethanol to dissolve the fuel varnish [I have an air compressor]
Dismount the Carburator, empty it, and clean it
Replace all the gaskets and anti-squeak pads (which have all turned to mush)
Install a sealed gas cap
Install a charcoal canister and connect it to both tank and carburator
What I would like advice on:
Is this a good plan?
Are there better ways to go about all this?
Can I clean the carb without dissassembling it? [I own a large sonicator]
Would you have a parts or manufacturer recommendation for the charcoal canister?
Should I replace the fuel pump or can it be cleaned? If it can be cleaned, is it worth the effort? If replacing it is easier, is there a better option for the pump without doing major gas line surgery?
How much flushing of the lines do I have to do - how fast does the varnish re-dissolve?
Since the sealing gas cap will make gas fumes build up in the tank, should I install a pressure release valve on the outlet line to the charcoal canister, such that only overpressure gas will vent? If yes, what is the PSI rating you would recommend?
Thank you so much for any help you can provide - this has been the car of my dreams since I was 15!
The engine bay, a beautiful garden full of all kinds of mold. Nature finds a way
Wide view of the underside of the tank; bottom of image is towards tail of the car
Underside of the tank, with the fuel level sensor leads and the fuel pump mounted right behind it
Front of engine - I am genuinely looking forward to meticulously cleaning all of this
From what I understand, if a charcoal canister was to be found, it would be tucked in the lower right-hand corner underneath the master cylinder. It is not there, and there are no mounting straps for one.
No charcoal canister never had one in 70 my car is also a march car and a ls5 must have been big block month I found the twin to my car on the corvette registry one vin number off also a big block car that car is in Germany
Hello M,
Welcome!
In the kindest way I have to say the photo you posted of the bottom of the tank and the gas supply shows a real mess.
Is your goal to go back to using the original type and location of the fuel pump, supply lines, sending unit, and gas tank?
Do you have any information that explains why the gas supply parts seem to be out of control?
Is there a reason the fuel pump isn't in it's typical location?
Regards......
Welcome to the Forum and being a Vette owner. I can tell that you are going to have a lot of work to do. All of your fluids, gas, oil, brake fluid and coolant and going to be in bad shape. It looks like there was a slow gas leak for a long time. I think you need to remove the electric fuel pump and install a mechanical pump on the engine. All of the rubber hoses in the fuel line should be replaced. On original GM fuel systems, they did not have rubber lines on the pressure side because of possible leaks.
I would guess that most of the other rubber hoses in the engine compartment and probably in need of replacement. It appears that you have a lot of clean-up to do, but it seems that it is mostly complete. Getting it back into shape will take some time and effort but should give you a sense of accomplishment when you get it done. An older Corvette is a lot of fun, but they always will need things done to it. I have owned mine for many years and I am always working on it, even when it really doesn't need anything done to it. Don't try to do too much at one time or you can become overwhelmed with the task. Do one thing at a time and then go on to the next.
I agree with the above. First thing to do is purchase an AIM. Assembly Instruction Manual. This is the manual used by the assembly line staff when building the car at the factory. The AIM is available from most of the major Corvette vendors. I would also order some of the catalogs from the same major vendors. Most have detailed diagrams of assemblies and sub-assemblies on the car. I would pay close attention to the front fuel lines and filter. That plastic filter could be dangerous. Perhaps the previous owner bypassed the stock mechanical fuel pump???? Jerry
If you are dropping the tank anyway, consider an in-tank electric fuel pump, and a fuel regulator. You'll be EFI ready for the future, but in the meantime, you'll be able to dial-in the fuel pressure for the carb. It seems that getting a mechanical fuel pump that works by itself is becoming much more difficult.
From: At my Bar drinking and wrenching in Lafayette Colorado
Unfortunately, the carb shown in the photos is a commercially rebuilt carb that is not likely the "correct" carb for the BB engine. Being commercially rebuilt, is is most likely hacked pretty bad with a slew of problems that are not financially viable to repair. The OP would be well advised to start shopping for a good, unmolested, rebuildable core. OP can also send me (e-mail or post) some more detailed photos of the carb, along with the carb number, and I can provide a better evaluation with recommendation for the best path forward.
Lars
Hello M,
Welcome!
In the kindest way I have to say the photo you posted of the bottom of the tank and the gas supply shows a real mess.
Is your goal to go back to using the original type and location of the fuel pump, supply lines, sending unit, and gas tank?
Do you have any information that explains why the gas supply parts seem to be out of control?
Is there a reason the fuel pump isn't in it's typical location?
Regards......
Hello!
My goal is to have it run reliably, and whatever needs to be done to make that happen, I'm ready to do. This car has been serviced almost every other month for at least the first 20 years of its life - we have receipts for all of it, mostly from the Chevrolet dealership (and at least some of that handwriting is legible) - so who knows what sort of macgyver stuff we'll find in there. I've classified all of the documentation and the binder is like 4 inches thick, and that's missing everything from the 90s on. The after market fuel pump isn't even the weirdest mod - she has an altimeter, and outside air flow thermometer, two kill switches, a block warmer, an extra extra battery charge meter, an oil pressure gauge mounted on the steering column, and a little receptionist bell under the hood because the horn is just too loud sometimes.
This car is already a big patchwork quilt, which I think adds to its charm, but I have no scrupules in making her a Corvette of Theseus if that means I get to drive her. I am fully prepared to replace the fuel pump, fuel hoses, fuel sensor, etc for modern versions. While I don't enjoy electronics in cars and am seduced by the idea of keeping her a fully mechanical beastie, I'd definitely prioritize keeping fumes and exhaust to an absolute minimum (she lives in our garage, where we spend a lot of time doing other stuff, like weightlifting and woodworking). If this means electrical sensors and fuel pumps - so be it, and no regrets.
Welcome to the Forum and being a Vette owner. I can tell that you are going to have a lot of work to do. All of your fluids, gas, oil, brake fluid and coolant and going to be in bad shape. It looks like there was a slow gas leak for a long time. I think you need to remove the electric fuel pump and install a mechanical pump on the engine. All of the rubber hoses in the fuel line should be replaced. On original GM fuel systems, they did not have rubber lines on the pressure side because of possible leaks. I would guess that most of the other rubber hoses in the engine compartment and probably in need of replacement.
Thank you so much! Excited to join the club
I am planning on draining her fully of all fluids available, as I assume none of it is even remotely usable. The gas leak makes sense - is that why it's all gummy and gross under there where the hoses and leads connect? I definitely figured all of that would have to be replaced. I fully intend to replace any and all parts made of rubber, and not just on the fuel lines; everything feels brittle and cracking all over the place, so even if they hold now it's better to just fully replace them with new material. I had spent a week at work diagnosing an electron microscope in my lab only to find out the rubber hose from the vacuum pump was old and full of cracks, which weren't apparent until in a fit of unscientific despair I shoved it out of the way to get to the high tension tank. You live, you learn.
It appears that you have a lot of clean-up to do, but it seems that it is mostly complete. Getting it back into shape will take some time and effort but should give you a sense of accomplishment when you get it done. An older Corvette is a lot of fun, but they always will need things done to it. I have owned mine for many years and I am always working on it, even when it really doesn't need anything done to it. Don't try to do too much at one time or you can become overwhelmed with the task. Do one thing at a time and then go on to the next.
This is only the start of the adventure! As much as I want a Corvette to drive, I am also very excited at the prospect of earning her loyalty by resurrecting her from her lonely oblivion. She belonged to my best friend's grandfather, so I got a good deal on her since they knew I intended to bring her back to her halcyon days of glory and "keep her in the family".
I have also been learning automechanic engineering, and it's been a really, really cool discovery. I don't think the average person realizes just how cool a car engine is. So I'm definitely looking forward to the work.
A 1970 Federal emissions car would not have a charcoal canister.
If you insist on a charcoal canister you will need a new California emissions tank, GM33D..
I would pay close attention to the front fuel lines and filter. That plastic filter could be dangerous. Perhaps the previous owner bypassed the stock mechanical fuel pump???? Jerry
Do you mean the in-line fuel filter on the line going to the carb? The housing is metal, and it looks really old. It has orange writing on the side, labeling the carb direction, and the rest is almost indecipherable, but I am fairly certain it reads GF-61. I would love to see what the deal is with the engine port that's supposed to house a mechanical fuel pump, but unfortunately the giant AC compressor is in the way.
Thank you for the manual recommendations - I have several repair manuals but none of them are as diagram-oriented as the AIM. I've ordered a copy, and one for the chassis overhaul as well.
From: At my Bar drinking and wrenching in Lafayette Colorado
1970 Corvettes do not use an in-line filter - you have another fuel system hack-job to clean up. The fuel filter is integral in the carb, and that in-line filter should not be used. You should have a single, steel hard-line directly from the pump to the carb with no filter in-line.
Lars
1970 Corvettes do not use an in-line filter - you have another fuel system hack-job to clean up. The fuel filter is integral in the carb, and that in-line filter should not be used. You should have a single, steel hard-line directly from the pump to the carb with no filter in-line.
Lars
Wow. This isn't the Corvette of Theseus, this is the Corvette of Dr Moreau. Might just do an EFI swap after all...
More pictures of the carb (7029200):
If you are dropping the tank anyway, consider an in-tank electric fuel pump, and a fuel regulator. You'll be EFI ready for the future, but in the meantime, you'll be able to dial-in the fuel pressure for the carb. It seems that getting
Thank you! With all the information and advice, I think I will replace the fuel system completely for something EFI-ready, which would mean swapping the gas tank, which is totally fine by me. The exhaust pipes have also seen better days - looks like this poor car has scraped itself on every curb available as she was driven from New Jersey to California in the 80s - they are flattened and dented and I was just gonna replace them wholesale too. Two birds, one stone, etc.
Hello M,
I'm still not clear just what you want to accomplish at this point.
You've mentioned EFI is that where you're headed?
Do you want to make it Calif. emission compliant for a 70 car?
How much effort and $$ are you prepared for at this point?
Seeing a few photos showing the overall car as it is now might help people give you some guidance.
Regards.......
I still don't understand the what, why and how of that 'stuff' hanging under the gas tank.
From: At my Bar drinking and wrenching in Lafayette Colorado
Originally Posted by Mishoulya
More pictures of the carb (7029200):
The carb is not the Corvette 427 carb - it's the carb used on Camaro & Chevelle 396 and 427 applications. There is no question that it has been commercially rebuilt, but it does not appear to be hacked really badly with "mix-n-match" major components. It appears to have its correct parts intact and in place for the carb number. Being a commercially rebuilt carb, it likely has some poor quality parts in it and a bad setup, but it looks like something that could be correctly set up and repaired. The Chevelle 427 carb is visually identical to the Vette carb, and can be set up to run the same if the commercial builder has not performed any irreversible mods to the critical parts.
Lars
The carb is not the Corvette 427 carb - it's the carb used on Camaro & Chevelle 396 and 427 applications. There is no question that it has been commercially rebuilt, but it does not appear to be hacked really badly with "mix-n-match" major components. It appears to have its correct parts intact and in place for the carb number. Being a commercially rebuilt carb, it likely has some poor quality parts in it and a bad setup, but it looks like something that could be correctly set up and repaired. The Chevelle 427 carb is visually identical to the Vette carb, and can be set up to run the same if the commercial builder has not performed any irreversible mods to the critical parts.
Lars
Mishoulya, Lars is a true expert with rebuilding and tuning Quadra-jets. If you send it to him, what comes back is 99.9% ready to go, maybe only requiring an idle speed adjustment for your engine. He tests and final tunes them on an engine he has in his shop – just for fine-tuning carbs. If you have a few weeks you can be without the carb, send it to him, you won't be sorry.
Thank you! With all the information and advice, I think I will replace the fuel system completely for something EFI-ready, which would mean swapping the gas tank, which is totally fine by me. The exhaust pipes have also seen better days - looks like this poor car has scraped itself on every curb available as she was driven from New Jersey to California in the 80s - they are flattened and dented and I was just gonna replace them wholesale too. Two birds, one stone, etc.
There are lots of threads showing what is needed to be EFI ready with a 70 fuel tank. You will need to pull it to clean what you have, at which point a new one is not expensive (compared to the rest of the EFI swap).
Here are two of many threads that might help get you started. 68-77 all used the same shape fuel tank. 78-82 is larger and easier to deal with, but best practice is to drop the tank either way. You might find your build sheet!
Do you want to make it Calif. emission compliant for a 70 car?
It is already. The OP should double-check, but I don't think CARB restrictions apply to vehicles made before 1976. And there are plenty of CARB-compliant EFI solutions.
Last edited by Bikespace; Mar 3, 2026 at 12:24 PM.
It really comes down to what the OP wants here. There is no need for a different tank here for EFI. A few different drop in EFI pump set-ups available that go straight into the original tank.
However, if Lars feels that Quadrajet can be saved. And flushing some lines, maybe a new fuel pump and a hard-line from pump to Carb would certainly be more affordable. Freeing up money for other needed repairs on the car.
Myself, I really like my EFI. But it wasn't free nor without time to get it all dialed in.
This is really easy.
Buy a new 49 state 1970 reproduction fuel tank with a sealed cap.
Clean the factory supply and return lines that run down the frame. (hopefully they don't leak)
Buy the correct mechanical fuel pump and hard line to the carb.
Send your q-Jet to Lars for a rebuild.
Forget about the charcoal canister.
Enjoy your Corvette.
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C3 1970 - Fuel System Overhaul
