I have a 1978 Chrysler with 400 engine with original Carter carburetor and lean burn system. Looks like I need to get the carburetor rebuilt. Should I rebuild or buy a new one? Would like to keep the lean burn on. Would the original work if I delete the lean burn later? Any new carburetor that would work with both lean burn delete or with lean burn?
Carburetor for 1978 Chrysler New Yorker with 400 engine
- Thread starter Fred A
- Start date
Justin Plant
Well-Known Member
lean burn carbs are lean burn carbs. I'm sure there is a member here that can guide you on getting it rebuilt. Lean Burn is not your friend. It'll be an up hill battle to the end.
Two things made the Lean Burn happen. A carburetor specifically calibrated to have a much leaner air/fuel ratio at cruise AND a timing advance curve calibration to have more advance to fire off the leaner mixture for reduced emissions (which is why no cat converter is on the car, as it was not needed to meet the standards). By 1980, the "lean burn" orientation was dead, but the electronics to run the distributor were still alive and well.
Even back then, to remove the LB system, it would take the then-available Mopar Performance electronic ignition conversion kit (which was sold by Chrysler itself, back then) and a non-LB carburetor.
The "trick" is in removing enough of the LB system electronics and wiring so that the new system can be easily installed. Back then, too, good aftermarket spreadbore carbs were not usually around with "aftermarket" calibrations, which could complicate things. Ending up with re-man carbs of undermined calibrations and of questionable quality, which resulted in the cars being sold "very cheap" to people who knew nothing about cars to start with (other than where to put the gas in and maybe check the oil). Result was that many nice cars went to an early and undeserved death.
Personally, I like the LB orientation of things. Just that as time progresses, the sensors and such can age and go out of production. In modern times, a Street Demon 650 carb (which has many cosmetic and engineering orientations of the Carter TQ carburetor) and a normal electronic ignition conversion kit are around.
As Chrysler now licenses the kit, rather than building it itself, can be problematic as some have noted a lower-quality control box being used. Sourcing a kit from Rick Ehrenberg's eBay shop can get the "good stuff", just not from Chrysler.
An ever more up-to-date deal would be to fully convert the fuel and ignition systems to a modern TBI self-learning EFI system and let the computer do the timing curve itself (which might use the existing LB distributor). Pricier, but the whole LB system would be modernized in one feld swoop. Might try Affordable Fuel Injection rather than Holley?
Just some thoughts and observations,
CBODY67
Even back then, to remove the LB system, it would take the then-available Mopar Performance electronic ignition conversion kit (which was sold by Chrysler itself, back then) and a non-LB carburetor.
The "trick" is in removing enough of the LB system electronics and wiring so that the new system can be easily installed. Back then, too, good aftermarket spreadbore carbs were not usually around with "aftermarket" calibrations, which could complicate things. Ending up with re-man carbs of undermined calibrations and of questionable quality, which resulted in the cars being sold "very cheap" to people who knew nothing about cars to start with (other than where to put the gas in and maybe check the oil). Result was that many nice cars went to an early and undeserved death.
Personally, I like the LB orientation of things. Just that as time progresses, the sensors and such can age and go out of production. In modern times, a Street Demon 650 carb (which has many cosmetic and engineering orientations of the Carter TQ carburetor) and a normal electronic ignition conversion kit are around.
As Chrysler now licenses the kit, rather than building it itself, can be problematic as some have noted a lower-quality control box being used. Sourcing a kit from Rick Ehrenberg's eBay shop can get the "good stuff", just not from Chrysler.
An ever more up-to-date deal would be to fully convert the fuel and ignition systems to a modern TBI self-learning EFI system and let the computer do the timing curve itself (which might use the existing LB distributor). Pricier, but the whole LB system would be modernized in one feld swoop. Might try Affordable Fuel Injection rather than Holley?
Just some thoughts and observations,
CBODY67
I have written a lot about lean burn in the past on this site. I was there at the time they were developing that system and in short it was a disaster and was a very big part of the company going bankrupt circa 1980. One ivory tower intellectual convinced the chief engineer at the time that if Chrysler introduced "lean Burn", they could save the money of adding a catalytic converter to their cars to pass the significant reductions in emission standards required beginning with the 1975 model years. All other manufacturers used catalysts except Chrysler in the beginning and ended up having to install a catalyst anyway. Unfortunately the lean burn cars could not pass emission standards and resulted in driveability that was so poor that the government forced a recall of their cars due to the fact that emission test cars picked at random couldn't follow the driving trace for the official test without passing out multiple times and forced recalls of some of the cars with Lean Burn.
The best thing you can do is convert the cars from lean burn and use a well calibrated carburetor such as the AVS II from Edelbrock or something from Holley. The driveability and performance will soar in comparison and your fuel consumption will improve too.
Dump the system completely.
The best thing you can do is convert the cars from lean burn and use a well calibrated carburetor such as the AVS II from Edelbrock or something from Holley. The driveability and performance will soar in comparison and your fuel consumption will improve too.
Dump the system completely.
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Would Edelbrock 1407 performer 740 cfm work?
When my Dad eliminated the Lean Burn system on his 1976 Dodge Royal Monaco in the early 1980's, I bought a Carter Strip Kit for a Thermoquad carburetor which contained parts to change the fuel/air mixture to get the best performance. I rebuilt the carb using larger jets and whatever else to enrich the fuel mixture. This made the car more responsive and didn't affect fuel mileage at all. I don't know if those are available today or not.
This is one option. The old Carter Strip Kits were great things to have. Do you recall the size of the metering jets and which rods you used?
The closest thing now available is the similar tuning kit for the Street Demon carburetors, available from Holley. Might be a bit pricey for just a few jets and rods, but less expensive than a complete new carburetor.
A close look at the Holley website of the metering rods might be needed to see if the SD rods will work with a Carter TQ carb, though. Although the Street Demon carb appears to be a clone of the older TQuad, there are some small differences between the two carburetors.
Would save the money spent on the throttle adapter bracket, too. The KEY thing would be the knowledge to learn how to change the rods.
Ideas from others?
CBODY67
Many might prefer an AFB over the newer AVS2, but the AVS2 carburetor is a more recent design and has better primary venturi designs. Both would work, though.
As to putting a square bore carburetor where a spread bore carburetor now is, on a spread bore intake manifold, that IS possible.
When I did an intake manifold upgrade on one of my cars, the aftermarket aluminum intake was cast for the spread bore carburetor, with both sets of stud holes on the carburetor base area. The manifold people said an adapter would be needed to put a square bore carburetor on the intake manifold.
At the time, I was not a fan of spread bore carburetors, but understood their possible attributes. I looked at their recommended adapter plates and got one. It was nothing more than an aluminum plate to cover the different size of the square bore carburetor. Some careful comparison and measurements revealed that a normal OEM-style thick, insulator carb base gasket, as was OEM on some truck motor engines we sold, would barely fit the spread bore castings of the intake manifold. It was as stiff as the aluminum plate and its two softer gaskets, so I tried it. It appeared it would work, so I carefully did it. It worked and contrinued to work for many 100ks of miles.
As to the factory cast iton intakes for TQuads, there is a video of how to cut-out/modify the primary side of the Chrysler factory intake to mount and use a square bore carburetor on them. Quite ingenious! On YouTube from a DIY guy's "318willrun" channel. Interesting! 318LA engines, but might work on some Poly318s, too.
But for pure bolt-on situations, the Street Demon would possibly be better. Just need the throttle lever adapter and some fuel line items to hook things up, plus the electric choke wiring. It is designed to work with square bore and spread bore intake manifolds. Which the Edelbrock carburetors are not. Of course, if you want to replace the intake manifold anyway, an Edelbrock dual-plane intake opens up the many other possibilities, too. Carb throttle adapter bracket would still be needed.
Something to think about,
CBODY67
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The TQuad works with the factory divorced choke where the choke thermostat is on/in the intake manifold. In some later models, it has an "electric assist" for that thermostat.
The aftermarket carburetors are available with a manual choke and also with an electric choke version, the customer's option. The electric choke is a better option unless the customer desires to install a manual choke cable and such into the car.
CBODY67
The aftermarket carburetors are available with a manual choke and also with an electric choke version, the customer's option. The electric choke is a better option unless the customer desires to install a manual choke cable and such into the car.
CBODY67
Only with an intake manifold that fits the carburetor. AND with a normal, non-LB, distributor, which might require some re-wiring to make it work.
For a 400 cubic inch engine, 750CFM is too much - you would be better off with a 650 CFM.
I would also get an earlier distributor from a 400 engine or 383 cu. inch.
@halifaxhops will have a good one for you that will give you a lot more spark advance that will give much more lively performance and much better fuel economy - the lean burn calibrations had too many vacuum advance delays or no vacuum advance at all under certain circumstances. His distributors are rebuilt and have many nos parts in them - you won't go wrong with his distributors. He worked on some for me and also had rebuilt ones that I couldn't find anywhere else and I was very pleased with all his help.
That was in 1982, so I don't remember the specifics. However, I went either 2 or 3 steps richer with both he jets and rods. It was a very worthwhile change at the time.
I have swapped out multiple Lean Burn systems and carbs over the years and the improvements were well worth it. Last one I did was on a 76 NYB with a 440 and we went to an Eddy AVS2 650CFM. Car never ran better however there is a bit of monkeying around with the kickdown linkages to get it right. You will need a squarebore adapter and the correct Chrysler linkage bracket from Edelbrock. I prefer the old Direct Connection Electronic Conversion kit but they are unicorns nowadays. I have also used the Summit and Proform kits with success. So in short here is what I would do:
Proform electronic Conversion kit Proform Parts 440-427 Proform Mopar Licensed Electronic Distributor Conversion Kits | Summit Racing
Edelbrock AVS2 with electric choke Edelbrock 1916 Edelbrock AVS2 Series Carburetors | Summit Racing
Edelbrock Mopar Linkage Adapter Edelbrock 1481 Edelbrock Throttle Lever Adapters for Performer Carburetors | Summit Racing
Edelbrock Spreadbore to Squarebore adapter Edelbrock 2696 Edelbrock Carburetor Adapters | Summit Racing
Non Leanburn Air Cleaner from an older Mopar for 4 barrel carb
Some have used a Pertonix conversion which is also a good alternative but a little more involved. You will need a FSM and have reasonable knowledge of basic wiring and how to set up timing/vacuum/idle as the Lean burn was doing this for you.
Good Luck!
Proform electronic Conversion kit Proform Parts 440-427 Proform Mopar Licensed Electronic Distributor Conversion Kits | Summit Racing
Edelbrock AVS2 with electric choke Edelbrock 1916 Edelbrock AVS2 Series Carburetors | Summit Racing
Edelbrock Mopar Linkage Adapter Edelbrock 1481 Edelbrock Throttle Lever Adapters for Performer Carburetors | Summit Racing
Edelbrock Spreadbore to Squarebore adapter Edelbrock 2696 Edelbrock Carburetor Adapters | Summit Racing
Non Leanburn Air Cleaner from an older Mopar for 4 barrel carb
Some have used a Pertonix conversion which is also a good alternative but a little more involved. You will need a FSM and have reasonable knowledge of basic wiring and how to set up timing/vacuum/idle as the Lean burn was doing this for you.
Good Luck!
Would Avs2 work with lean burn?
There were no oxygen sensors on the lean burn vehicles since they were just mechanical devices back then too, but were calibrated to burn lean. All the lean burn computer really did was to control when the system added or subtracted any vacuum advance under certain operating conditions. Usually subtracting or minimizing spark advance was its purpose because when ignition timing is retarded, both hydrocarbons and nitrogen oxides are reduced compared to plenty of spark advance operation and it also causes increased fuel consumption compared to running with plenty of advance and of course acceleration is affected in the same way. The Carter Carburetor and Holley reps who were stationed mostly full time in Chrysler's fuel systems lab told management that they could not hold the production tolerances that the self proclaimed genius of the system, Gorden Fenn, specified. The chief engineer at that time of powertrain was under severe pressure to save money because the Corporation was going broke and managers who could save money were hired for the top positions in the company. The Formals in particular during the design development were also "thrifted" in every way possible to minimize the costs of building the vehicle as a result too. Everything on the formals was squeezed to the limit to save money and that is why the dash panels are chintzy, there were plenty of water leaks and even the tilt steering columns were "thrifted" that GM sold to Chrysler and there were a flood of complaints from all the dealers due to those vehicles being constantly in dealership repair facilities due to premature need for repairs compared to previous models. This guy Gordon Fenn convinced the chief engineer that the company could eliminate the catalytic converter and still pass the new more stringent emission standards so of course he got the nod and was a kind of ivory towered intellectual with little real would experience. So in the end, the lean burn cars did not meet emission standards with just Lean Burn and then the company had to install both a catalyst as well as continue with the already developed "lean burn" hype and customers hated the driveability problems, excess fuel consumption and use of cheap components as well that drove those owners to the service department way too soon compared to previous corporate practice in terms of durability.
So for the above reasons, I recommend putting on an AVSII carburetor of about 650 CFM (and attendant intake manifold changes as needed) and get a distributor from the 1970 - 1971 timeframe and use that instead of the lean burn junk or maybe an aftermarket spark control system instead of the lean burn computer.
Those formals and all the attendant problems with them substantially caused the corporation to go bankrupt and then Lee Iacocca took over and over time righted the ship. I saw it all taking place. That is when I exited the corporation after over a decade of time with Chrysler. It was a sad time for me when I left.
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