Lawn Mower Carburetor Improves Mileage On Old Sedan

Before the Ford marketing department started slapping Maverick badges on pickup trucks, the name had been attached to compact cars from the 70s instead. These were cheap even by Ford standards, and were built as a desperate attempt to keep up with Japanese imports that were typically higher quality and more efficient than most American cars at the time. Some people called them the poor man’s Mustang. While Ford and the other American car companies struggled to stay relevant during the gas crisis, it turns out that they could have simply slapped a lawn mower carburetor on their old Mavericks to dramatically improve fuel efficiency.

The old Maverick used a 5 L carbureted V8 engine, which is not exactly the pinnacle of efficiency even by 1970s standards. But [ThunderHead289] figured out that with some clever modifications to the carburetor, he could squeeze out some more efficiency. By using a much smaller carburetor, specifically one from a lawn mower, and 3D printing an adapter for it, he was able to increase the fuel efficiency to over 40 mpg (which is higher than even the modern Mavericks) while still achieving a top speed of 75 mph.

While it’s not the fastest car on the block with this modification, it’s still drives well enough to get around. One thing to watch out for if you try this on your own classic car is that some engines use fuel as a sort of coolant for certain engine parts, which can result in certain problems like burned valves. And, if you don’t have a lawnmower around from which to borrow a carb, take a look at this build which 3D prints one from scratch instead.

Thanks to [Jack] for the tip!

71 thoughts on “Lawn Mower Carburetor Improves Mileage On Old Sedan

  1. Saw this by accident on youtube last week.. One of those videos, just for the reason of uploading it to youtube?
    The mixture will be so lean, the engine will probably last not very long.. There would be plenty of more practical ways to improve the mileage. This is not one I would consider.

    1. I’ve watched the video and even with a very critical eye. You’re not actually correct. He’s modulating the mixture with an Arduino that is controlling an old Chevy Idle Air Control that lets in air as needed, and he’s running the carb intentionally rich if I recall, letting the IAC do the work of maintaining the mixture, based on input from an O2 sensor. He actually built an app for his phone that shows him the mixture in real time, and it’s around 12-15:1 just like a normal engine.

      1. He is using a computer controled air bleed system to lean the mixture out. This isn’t legit with the epa. Air bleed system tend to generate lots of Nox pollution.

        1. Wrong, HIGH COMBUSTION TEMPS is what causes an excess of NOx particulates which generally only occurs with a very lean mixture, excessive engine load, poor cooling, etc. He is controlling the mixture to 14.5:1 under all driving conditions which is a nearly ideal stochiometric ratio.

    2. “The mixture will be so lean,”
      a too lean mixture will not ignite, period.
      it is an old myth that running lean mixture will wear or ruin an engine. it is not the lean mixture but overheating. at WOT, rich mixture will help cool the engine from the inside and avoid overheating, but at part throttle you can lean down to the engine quitting and the engine wont care

      1. What?

        Para: ‘Lean mixes don’t ignite. Lean mixes don’t destroy engines, it’s the high temp from lean mixes that destroys engines.’

        Did you read what you posted? At least you sort of corrected yourself.

        Put clearly: Lean mixes _destroy_ gasoline IC engines. Glowing hot headers are a symptom. Don’t do that.

        However, on point. This thing isn’t necessarily lean. It’s just an old school analog rev limiter. They put tiny carbs on engines back in the day to make it impossible to overrev them. Bet this engine can’t rev past 1500 RPM. Might as well just get a four banger and save the weight.

  2. Honestly struggling to wonder why a 5L engine was considered necessary? This isn’t a pick-up truck.
    I know modern engines are more efficient than old ones, but 2L should be enough for a compact car?

    1. Because “there ain’t no substitute for cubic inches”?
      Well, actually there is, namely clever engineering, but that had not caught on yet in seventies USA.
      I mean, a five liter V8 in a cheap car? In Europe you’d find that only in real high end cars, especially in the seventies.
      I remember when I was around ten years old my father got a Chrysler 2l and that was considered a big engine in those days.

      1. Oh also. They are super simple and easy to work on. I had a 1966 Mustang with 289 ci V8, with a pretty humble set of standard tools you could do/fix pretty much everything. Once tolerances get higher you lose ability to do that.

      2. 5L Mavericks were not at all common in this time period unless specially ordered in specific variants or swapped. The much more common engine was an inline 6 of either 170, 200, or 250 cubic inch.

        1. I was going to say the same thing. My father had the slant six, and the carb was not too far off from lawn mower specs.
          And yet he used to drive it like he was in a race every where he went. I’m pretty sure the passenger side fire wall had foot impressions from all of us unlucky to be passengers, always subconsciously attempting to mash the nonexistent passenger brake pedal.

      1. “practically free?” Oh, I don’t know. In 1971, maybe, when I recall lawnmower gas was $0.25/gal. By 1979 it cost a day’s minimum wage to fill up my Plymouth Fury. Even with this week’s prices, that same car (Rest In Pieces), would cost *less* than a day of minimum wage to fill up: In terms of hours of minimum wage per gallon (or litre), gasoline is cheaper now.

        Now, a modern car can go 2x further on the same amount of fuel (but likely can’t carry 13 teenagers like my Fury did once)

        1. Umm, 1971 was 15 cents a gallon in smell-A, 11.9 @ gas war stations on adjacent corners. Two bucks filled an average four door sedan, three bucks for all night cruising Van Nuys blvd before the three light lightposts were installed.

          1. We had imperial-size gallons here in the Great White North, not those stunted american-size ones, so of course they were more expensive. Not so sure about the size of the dollar at the time, but I’m sure taxes were higher here too.

          1. The back seat of my 2 door 60 Saratoga is a king sized bed. The trunk is a short pickup truck bed. 6 mpg of carbureted 383HD rolling art.

            Chrysler land yachts were gone by 70 though. A Fury was a compact car in comparison.

      2. Practically free…except it wasn’t. Looking at the cost of gasoline in the 70’s to today isn’t an accurate way to compare the cost of procurement. Inflation is the reason the gasoline price shot up. Relatively speaking, you are still buying the same amount of gas today for the same scaled value in currency of the 70’s. A single dollar was worth almost 7x more than today. It works out to a yearly decrease in value of around 4%. It also means your paycheck as a gas station clerk was 7x less. That, Craig, is why gasoline in the 70’s seemed free…but the people buying it back then would beg to differ.

        1. Ah, Yeah. Inflation. I guess you pay about a dollar a gallon for gasoline now? Cause if you’re factoring in inflation, then that’s what a gallon SHOULD be today, instead of $5.

      3. It’s changed to no longer in production, circa 2002. Ford went all in on overhead cam V8s while GM refreshed their 1960’s V8 by copying Ford’s cylinder heads and doing some other tweaks.

        The Chevy small block V8 long suffered with having an EI IE EI IE valve pattern that placed two exhaust valves together in the center. Many of their cast iron exhaust manifolds had one large runner in the middle and a small runner at each end. With head and manifold or exhaust header designs that fully separated the middle exhausts, they still had issues with running hotter in the middle.

        Eventually, around the time Ford was starting to phase out their old Windsor V8 engines, GM switched theirs to an EI EI EI EI valve pattern, which makes it harder to spot when someone has abused a classic Ford custom car or hot rod with a Chevy implant.

      4. “Practically free” only in comparison to today’s prices.

        A common complaint back in the 1970s was that jobs were hard to find, and if you did find one it didn’t pay enough for you to put enough gas in the car to drive to work every day.

    2. This was near the epitome of “70s emissions controls” which consisted of lots of sill black magic type things that amounted to “de-tuning.” the engine was probably desined to produce 2x the power but limited by things like intake restrictions etc. So they’d just stuff the bigger, heavier engine in the small car and call it “efficiency”.

      Also, this was probably the “bigger engine option” in this car.

    1. it won’t necessarily run lean and burn the valves, but it certainly will not flow enough air to make much more power than the mower it’s from did.

      There’s always a trade off, there’s a guy doing the opposite (small ICE in a prius)…go kart engine and does about 50mph with “great mileage.

  3. 1/4 mile time slip with video, or it didn’t happen. He did get some good mileage, but time will tell if this is/ would have been useful. If for nothing else, assuming compact car gas mileage, it still sounds nice.

  4. I know of at least one ford Maverick that had a Lincoln 460cid engine stuffed into it. No idea what all they had to do for that; the two times I met the vehicle it was not operable because of parts broken by the previous test run. I got to see a county sheriff tell the owner “If you take that thing out on my roads again I’m arresting you for reckless endangerment.” Probably justified.

    1. Ford maverick with a 460? Pfffffffffft. Driving down the road and had to do a double take on some cars in a driveway. I turned the car around and went back to look at the wonders I had seen. 4 hot rods parked side by side. The one I wanted to see was a nash rambler with a blown and nitroused 460 in it. Rear end was tubbed with a ford 9 inch and the rear tires were so wide you almost couldn’t see the diff. Owner came out and we talked for a while. The previous owner of the four cars had won the lottery and started to build the cars. He had over a half a million dollars in the four cars before he went broke, his wife left him, and he lost his house. The gent I was talking to had bought all four cars 120,000 dollars or about 30,000 for each. I asked him how the nash handled. His response was classic, “it doesn’t”. He said as soon as you got on the gas the car would just start to going sideways or just spin out. Man, was it ever the coolest thing i had ever seen though!

        1. That is cool!!! I have seen several builds of taking single cylinder Briggs and Stratton horizontal shaft engines and welding them together but that bike is cool!!! It uses a pony motor for starting even!!!

    2. When starting a project, the primary consideration should be lightness of the chassis.

      Your going to have to subframe it, tub the back and replace the front clip with fiberglass anyhow.

      Which is why racers love box novas, pintos, mavericks and 1950s Fiat 500s.

      Only going a 1/4 mile, don’t need no stinking cooling system, passenger seat or interior. Nothing that doesn’t make the car go faster, except the roll cage.

  5. installing a small carb does not make an engine run lean, given that the carb is properly adjusted. it is the equivalent of running with a small throttle opening.

    so the same could have been achieved by placing a block under the accelerator pedal, discounting the influence that has on the transmission. there is nothing magic, black or otherwise, going on here.

      1. depends how he’s controlling the air bleed, it could be used closed loop with a lambda sensor to achieve a correct mixture. Closed loop control was done like that right before electronic fuel injection became the norm

    1. Now there’s a subject for a HaD article, How does NASCAR make cars go 200+ MPH at Daytona and Talladega while the engine is sucking air through four holes smaller than a US quarter coin?

    1. My dad bought a (used) 1971 or 72 Mercury Comet GT for my mom. It had a 302 V8 and the automatic. Very front-end heavy in a rear wheel drive, not good at all in snow, and hydroplaned in heavy rain. By the time she had it, I was already in college and didn’t drive it much until after she passed away in 1978. Certainly more fun to drive than the lime green Pinto station wagon they had.

    1. Pontiac told the government where they could shove it for a couple of years with the 1972 and 1973 “Super Duty” package on the Trans-Am.

      Since “one ton” trucks were exempt from emissions controls until sometime in the late 80’s or early 90’s, Dodge in 1977 and 1978 made the Lil’ Red Express and Warlock pickup trucks with unrestrained big V8 engines.

    2. My brother’s wife sold me her 1984 Pontiac Gran Prix sometime in the 90s (V8-at least a 305, but knowing my brother, it might have been the 357). It was like driving a gunboat to university and work and teenagers to whatever. Cushier than some other vehicles I have had, and I’m not one to do justice to a V8, so gas mileage was ok.

      But one evening some kid with a sporterised VW Jetta stops next to me at the stop light, revving his engine at me. And this 40 something mom decides to show the child just how hot his car really was next to the aging glory of a vintage V8. No tire chirping, just a smooth application of power, and the kid has his engine screeching like tormented hamsters as I left him behind. Thus ended the lesson about taunting middle-aged women.

      Then my daughter started driving it, and it gained a number 5 in a circle on the door, and she gained a number of points on her license. Until the transmission disintegrated….

      1. In the late 1970s, we had an early 1970s Plymouth Fury III as a family car. It had one of the bigger engine options – the 400 or 440 cubic inch.

        My mother drove it most of the time. Thinking back, I’m not sure how she could even see over the steering wheel. I was 11 or 12 years old at the time and as tall as she was.

        She didn’t make much use of that big V8. She just drove us kids around and grocery shopping and such.

        One year, my dad put some cyclone wheels on it. The wheels could be used on cars with different bolt patterns. You had to put a special washer under each nut to make it fit the different patterns.

        One of the washers got lost while changing tires later that year. Mom loaded us kids into the car and we drove across town to the only shop that sold the special washers. It was a specialty shop that sold parts to hot rodders and racers.

        Little lady walks in with four kids in tow and buys one washer.

        I put it on the car in the parking lot before we started for home. The parking lot was just a row of parking spaces in front of the shop. Basically just deep enough for a single car and maybe three feet between the back end of the car and the road.

        Maybe 50 feet from the shop was a small rise in the road. You couldn’t see cars coming behind the rise.

        Mom backed out, and had the car about half in the road when some yahoo blasted over the rise at an insane speed.

        She dropped the car into drive and floored it. She left a huge cloud of smoke on the road, and turned the car sideways in the parking lot in front of the speed shop. The yahoo just barely missed the tail end of the Plymouth.

        Mom put it in neutral, took a deep breath, and drove home.

        I’ve always wondered what the guys in the speed shop thought of that number.


        That big V8 hated summer time heat. We lived in Louisiana and later moved to Arkansas and then Texas with the Fury.

        On really hot days, the lower radiator hose would get too hot and soft. It’d sometimes smash flat when accelerating away from a stop light. The temperature gauge would shoot up, and mom would have to ease off the gas until the hose popped back into shape and the coolant could flow again.

    1. 4000 pounds is _not_ a land yacht. Compact car.

      Have you ever seen a 50-60s land yacht?
      Mine is 6000 pounds, 2 doors. 383 high deck (small bore proto 440).
      Not much fun to drive. Drum brakes and everybody is looking at you trying to figure out WTF it is, not paying attention to their driving.
      But they were banned from demolition derbies because plate steel vs sheet. Newer cars bounce off totaled, don’t leave marks (true story from previous owner).

    2. Gran Fury, Newport, New Yorker were all full body cars up to 1980. My favorites were the fifth gen.(69-73).
      The one from “Thunderbolt and Lightfoot” always brings a smile to my face.

  6. I’d ask if there’s an injected version of that engine or injection manifold that will fit – that plus Megasquirt or Speeduino would let you run a much much better tuned system with closed-loop operation when cruising using a lambda sensor as feedback.

    That would give you all the economy when you’re driving gently, but with full power available when you floor it, and probably much more driveable and reliable too – at least that’s my experience across multiple Megasquirted vehicles over 10’s of thousands of miles.

  7. First part: what’s old is new again. Instead of a lawnmower carb, back in the 1960s you could order restricter plates for Quadrajets, Carters, Holleys, etc. from the JC Whitney catalog and accomplish pretty much the same thing by reducing the CFM available for induction. I don’t know how well they worked. You can probably still get something similar from Jegs or Summit.

    Second part: Why of course, the hacked Maverick obtains better economy. Not only is the flow restricted, the owner has installed a closed loop computer controlled fuel system. Back in 1970 you could get a Bosch transistorized analog computer fuel injection system, but it probably would have cost more than a whole new Maverick.

    The majority of Mavericks were equipped with straight six engines. As a teenager, my friend’s parents had a Maverick and it was about as spartan as a car could get short of Kaiser Henry J territory. Honda and Toyota didn’t have much to worry about in competition from the Maverick. I lived in the Midwest US, and Mavericks were sort of disposable cars, rusting furiously to the point of being ready for the scrap yard in fewer than five years. The early 1970s were a low point for US auto manufacturers’ quality standards, even on pricier models. Ford finally scraped the bottom with the Pinto, but that is another story.

  8. Great to see good ole Uncle Luke getting some deserved attention. If you go back and watch the whole video series he explains most of the process. To my recollection, most of his projects are pretty good about giving the details on how it was done and why he did it that way.

  9. Wow!
    I’m disappointed in the Hackaday crew on this one. It’s like no one bothered to watch the video series before running to these comments to spew opinions and criticisms based on complete falsehoods!
    1) The engine has an electronic AFR monitor. That output is used by a custom electronic controller that keeps the AFR in line under all conditions. It is NOT run lean. Period.
    2) The vehicle runs fine and certainly is capable of exceeding 1500 RPM.
    3) It generally isn’t RPM limited, it is LOAD limited. Or if you want to think of it another way, it is acceleration limited.
    IE it can go 70+ MPH, but it (probably) can’t tow a trailer up a hill at the speed limit.

    This is a proper hack and should be getting a lot more positive feedback from this group. The guy did the math, anticipated the problems, created devices and software to overcome those problems. He tested his hypotheses, collected data, and corrected based on those observations.
    In other words he used the scientific method, properly, to perform an experimental “hack” on an engine and created custom, unique parts and modifications to make it work as intended. That sounds like a good hack to me.
    Go actually watch the series and learn how he did it.

    1. FINALLY a commenter in here that understood. Luke did this originally for fun and his own curiosity. So obvious how many people first jumped on the keyboards without watching. Also need to watch the prior videos on the maverick and this carb project before they’re qualified to say anything.

  10. Having tuned live programmable ECUs for fuel economy, fuel atomisation and air speed into the cylinder have a bearing on economy and drivability. Prior to stricter emissions, alot of engines used to run very lean at idle and cruise from the factory and had good economy. Nox emissions required engines to run at richer at stoich and raised fuel consumption. The increase in fuel consumption with this setup would be from a good atomiser mixture and running lean. The small barrel would have little benefit of air spread at the valve. You could achieve the same with high atomising injectors at the valve running lean.

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