Some of us in the old car hobby remember the days when cars had steel dashboards, no air bags or safety belts, and a collision avoidance system was paying attention to driving instead of texting or yapping on a phone. Most vehicles had neither power steering nor power brakes. Many, in my part of the country, didn’t even have heaters. An AM radio was a luxury item, and windows were rolled up or down by hand cranks.
As kids, we seldom rode in child safety seats, but often in the beds of trucks. We ate Twinkies, Sugar Pops, Sugar Smacks and real butter (if our parents could afford it). We drank sodas, Kool-Aid and milk that didn’t taste like milk-flavored water. We built a lot of our own toys and invented things in garages or barns filled with chemicals and old motor oil. We used our dads’ electric drills, saber saws and bench grinders, most of which had enough power to pull a Sherman tank out of quicksand.
We didn’t tell our parents when we had life-threatening accidents, because they would douse our wounds with iodine… or, worse, might take us to a doctor. About the only good thing about going to a doctor was he didn’t tell us to lose weight.
Just about every boy—and more than a few girls—were mechanics, because we had to fix our old things instead of buying new ones. If we weren’t already mechanics, we quickly learned how to be when we bought our first cars.
Of course, this is just another version of, “When I was your age,” and succeeding generations will have their own. But how does this relate to carburetors and buying old cars and trucks?
Several years ago I bought a very nice 1964 CJ-6. I had my eye on this Jeep for over a decade, because it seemed to spend most of its time sitting at a gas station. I had asked the gas station owner several times if it might be for sale, but he always just smiled and said no. Then, one day, a friend called to say he’d seen this Jeep sitting by the road up the coast with a “For Sale” sign on the windshield.
Having a bit of extra green at the time, I loaded my tow bar into my Nissan Patrol and drove up to investigate. The gas station owner had retired about a month before and had sold the Jeep to a twenty-something guy. The Jeep’s new owner—who was obviously not a horse-trader—told me it was a “worn-out piece of junk.” In fact, his asking price was $ 500 less than he’d paid.
I was amazed because, except for normal aging and wear, the Jeep was in almost perfect condition with just over 50,000 miles on the odometer. The steering and front end were tight, the brakes were excellent and it didn’t even jump out of second gear on compression. The engine, an F-head Hurricane, instantly started cold on half-choke. Being a reasonably honest person, I asked the guy why he thought the Jeep was worn out.
The first clue should have come when I started the engine. The guy looked surprised and said it had never started that easily before. Apparently he didn’t know what the choke was for! After his title and my cash changed hands, I asked him more about why he thought this Jeep was worn out.
He said, “It was hard to steer, and the transmission was certainly worn out, because it made a whiny sound.” He also said the gears always ground when trying to shift and it leaked oil. Besides being hard to start cold, the engine was also sometimes hard to start warm. And, to him, it had no power. The Jeep wouldn’t do much over 60 mph, and it held up traffic whenever he was climbing hills so people honked and flipped him off. He said the windshield wipers didn’t even work for him half the time.”
No doubt many readers of my own and older generations are chuckling. Here was someone who’d bought a vintage Jeep and expected it to perform like a modern SUV. The same sort of scenario is increasingly played out by younger newcomers to the old car and truck hobby: They buy a Model A Ford or a 1957 Chevy and are unhappy when they find it to be slow, noisy, temperamental and leaky.
REMEMBER: IT’S A VINTAGE VEHICLE
Some might say it’s their own fault because they didn’t do their homework and learn about older vehicles before buying one. Some might also say they had uneducated expectations about how the vehicles would perform, what they could be used for and how they had to be treated and maintained. This is understandable in the case of that CJ-6, because the guy wasn’t looking for a classic vehicle. He had only wanted a Jeep to go four-wheeling, and to use as a second car. It’s hard to blame him for that, because a 1964 CJ-6 doesn’t look much different from a 1980s, 1990s or even a current model. However, such lack of self-education is harder to forgive when it comes to someone who wants a vintage vehicle.
One could say that everything that was “wrong” with that CJ-6 would also be wrong with the majority of other vehicles in the old-car hobby, i.e., it “was hard to steer” because it didn’t have power steering, and it was hard to start when cold because its owner didn’t know what a choke was for…Or understand what a carburetor was all about. And sometimes it was hard to start when warm because he flooded the engine.
Compared to most of today’s vehicles, it “had no power” because its four-cylinder engine had only been born with 72 horses. It wouldn’t go much faster than 60 mph because that was as fast as it was designed to go. The transfer cases of older-model Jeeps and prewar vehicles always whine to some extent. The transmission ground when shifting, because even though it was technically a syncromesh, I have seldom seen an older Jeep that didn’t shift more smoothly by being double-clutched. The transfer case dripped a bit of oil from the rear output shaft because—though it technically wasn’t supposed to—most such units do. And, of course, the windshield wipers were operated by engine vacuum, so they slowed down or stalled when climbing a hill.
Had this guy kept the Jeep, he would have probably found many other things to be unhappy about. If he took it to a quick-lube joint, he might have been billed for extra grease and gear oil, because it had so many lube fittings and gearboxes. This is assuming that the quick-lube people were knowledgeable enough to check not only the transmission, transfer case and front and rear differentials, but also the front axle ball joints. There may have also been a problem when it came to finding a replacement for the bypass oil filter element, not to mention servicing the oil bath air cleaner.
There probably would have been more unhappiness if the Jeep had needed a new or rebuilt generator (not an alternator), a voltage regulator, a starter, a water or a fuel pump, because most of these items wouldn’t be found on the shelves of typical auto-mart stores. But, again, this guy hadn’t been looking for a classic vehicle, so one probably shouldn’t blame him for unrealistic expectations.
On the other hand, if one is looking for an historic vehicle, then it is certainly up to him or her to educate themselves well in advance of making a purchase.
If you’d to get into the hobby, the following information might drop a little knowledge about what to expect when buying a carbureted vehicle.
‘CHOKING’ ISN’T JUST A WRESTLING FOUL
First, what is a carburetor and why does it need to be “choked?” A carburetor’s basic purpose is to atomize liquid gasoline into a vapor that can be burned in the engine to produce power.
“Atomize” might sound like something from “Honey I Shrank the Kids,” but it simply means transforming a liquid, such as gasoline, into tiny particles. In a fuel-injected engine—as most modern vehicles have—this happens as the gasoline is injected, or sprayed, into the cylinders by the injectors. In a carbureted engine, atomization is accomplished by what is called “venturi-effect.”
A venturi is a restriction, or narrowing, of a passage. Air that is pulled into the top of a carburetor—the throat—by the vacuum created when the engine’s pistons go down on their intake strokes must pass through this venturi. The air speeds up at this point, because the same amount of air has to get through a smaller space. This creates a suction. A nozzle is fitted into this area and connected to a fuel reservoir within the carburetor, commonly called the bowl. The suction in the venturi draws liquid gasoline out of the nozzle where it’s atomized in the air rushing down the carburetor throat.
The atomized gasoline mixes with the air, which creates a flammable vapor. This vapor is pulled into the engine’s intake manifold where it is distributed by the opening and closing of valves to each of the engine’s cylinders. Once in the cylinders, the intake valves close, the piston comes up on the compression stoke, a spark plug sparks, and the vapor ignites and burns. This burning creates pressure which forces the pistons down on their power strokes. This turns the engine’s crankshaft, and you drive off down the road.
That was the “Kid’s Club” version, but even though the relatively simple carburetors of most common vehicles are much more complicated and have many more parts than the accompanying illustration, it is still the basic principle on which all carburetor-equipped engines operate.
In most of today’s electronically controlled fuel-injected engines, an on-board computer determines how much fuel is needed at any given time, from when an engine is idling at a stoplight to driving down the freeway at 80 mph. On the other hand, in a carburetor-equipped engine, fuel delivery is accomplished by mechanical means, such as butterfly valves and accelerator pumps, and the only brain in a carburetor-equipped vehicle is the driver.
Primitive as they may seem, carburetor-equipped vehicles managed to perform quite well—and still do—for over a century. Not to mention soldiering through many wars. However, this isn’t an article about repairing or rebuilding carburetors, because that would take a book, and the proper book—or manual—for your own particular vehicle is something you should have. Instead, it’s a basic primer on how to understand your vehicle’s carburetor.
EACH IS UNIQUE
Like the vintage vehicles they power, carburetors are a lot like people: each is an individual with its own personality. Just as when living or working with someone, having a happy relationship with a vintage vehicle means learning about what makes it happy… as well as what doesn’t. For the twenty-something guy with the CJ-6, it was an unhappy experience when he got in his Jeep the morning after he’d bought it, turned the key and it wouldn’t start.
We already know that he didn’t understand the function of the mechanical choke, but being from a generation that grew up with fuel-injected cars, he also didn’t pump the accelerator once or twice before using the starter. Doing so would have squirted a bit of liquid gasoline into the carburetor throat by a mechanism called the accelerator pump. This might have made the engine start whether or not he had used the choke. Why?
Because a cold engine needs a richer mix of gasoline and air to start and run until it warms up. In other words, there has to be a bit more gasoline in the mix. Again, in a fuel-injected engine, the proper mix for cold-starting is determined by a computer, but in this case, the driver was the only brain on board. By pulling the choke knob on the dashboard, he would have closed a butterfly valve in the top of the carburetor throat. This would have restricted the amount of air that could enter, so the fuel/air mix would have been richer in fuel. How far the choke knob was pulled out would determine how much the valve in the carburetor closed, and this is something that could only be learned from experience, and with that particular Jeep.
Some vehicles have vacuum-operated accelerator pumps. This means that the pumps won’t squirt fuel into the carburetor throat unless the engine is running, so proper use of the choke is vital to successful cold starting.
Probably the most important thing to understand about vintage vehicles—even if you have an operator’s manual (and you certainly should!)—is there is only so much you can learn from a book. The rest has to come from experience with each individual vehicle.
For example, even if two 1942 Willys MB Jeeps were brand-new on the factory lot, each would have slightly different operating characteristics that would affect many aspects of how they started and operated. Parked side-by-side on a cool morning, one Jeep might start more easily with the choke knob pulled halfway out and after pumping the accelerator pedal once. The other Jeep might start more easily with the choke pulled out all the way and after pumping the accelerator pedal twice. If the morning was warmer or colder, or if it was raining, each Jeep would require a different choke setting, or no choke at all, and likewise more, less or no pumps of the accelerator pedal.
Each Jeep would also probably have slightly different characteristics when it came to starting them after their engines were warm. While neither Jeep would probably need any choke, one might start easier with a slight pump of the accelerator pedal, while doing so to the other Jeep might flood the engine and make it hard to start.
A FLOOD OF ADVICE
What is flooding an engine? Flooding is the opposite of what happens when you don’t use the choke and the fuel/air mix doesn’t contain enough fuel for the engine to start cold. Flooding means there is too much fuel and not enough air for the fuel to ignite and burn.
You can flood a cold engine by using too much choke and/or pumping the accelerator pedal too many times. It’s usually easier to flood a hot engine, because the engine doesn’t need as much fuel to start.
APPLYING THE CHOKE
This brings us to the proper use of the choke for those who have never owned or driven a vehicle equipped with a manual choke. First off, don’t feel bad about it, because automatic chokes came in to wide use on cars during the mid 1950s. By the 1960s, they were also being fitted to most light trucks.
Most operated by manifold heat, having a chamber with a spiral spring, and the spring would expand as the engine warmed up. With the engine cold and the spring tightly coiled, the choke butterfly valve was closed. After the engine started and began to warm up, the expanding spring would gradually open the butterfly.
If properly set, these chokes usually worked fairly well. As vehicles aged, however, the chokes often got out of adjustment and became one of the most effective items ever invented to shorten the life of engines and waste gasoline.
Why? Because many didn’t open the butterfly fast enough as the engine warmed up, resulting in too rich a fuel/air mix, so the excess fuel didn’t get burned. The the unburned fuel ran down the cylinder walls, washing off the lubricating oil and causing rapid wear of the piston rings and cylinders, as well as diluting the oil in the crankcase, causing excessive wear of many other engine parts.
Many aging automatic chokes also didn’t open the butterfly all the way, resulting in too rich of a mix at all times and wasting gasoline. On the other hand, some automatic chokes failed entirely, making engines difficult to start when cold. Not surprisingly, there were many aftermarket kits available during those times to convert automatic chokes to manual operation.
So, do you properly use a manual choke? First, you must get to know your own vehicle. You must realize you have the only brain on board. You must pay attention to how your vehicle behaves in different cold-starting situations ranging from a warm summer morning to a zero-degree winter night. Again, while you will have to find the most effective choking procedure yourself, here is a basic guide until you gain that experience:
Assuming a fairly cold day, pull the choke knob all the way out before cranking the starter. As soon as the engine starts, begin easing the choke knob in by gentle degrees until you find a position where the engine idles smoothly. Leave the choke in this position for about 30 seconds, then ease it in a bit more until the engine’s idle just begins to falter. Leave it in this position until the idle smooths out again—as the engine warms up—and repeat this procedure until the engine is idling smoothly with no choke at all.
In most cases, this warm-up will take about 5 to 10 minutes. Giving your engine time to properly warm up at idle will greatly prolong its life. And remember to never rev a cold engine.
As already mentioned, the exact procedure for your own vehicle will vary. For example, you may find that your vehicle starts best in most cold-start situations with the choke knob pulled only halfway out. Some vehicles will cold-start with one or two pumps of the accelerator pedal and no choke at all, but then will require choke to keep running. In any case, always use the minimum of choke, never rev the engine and push the knob all the way in as soon as possible.
Related to not revving a cold engine, some later-model manual chokes also opened the throttle to some extent to make the engine idle faster…in many cases it was too fast. However, most of these chokes can be adjusted to slow down the idle without affecting choke operation, and the slower a cold engine idles, the better.
How do you know if you’re using too much choke? The most obvious indication will be a “loping” or “galloping” rhythm of the engine at idle. While hard to describe in words, you will know it as soon as you hear it; and it will be a much different sound than the engine makes when not getting enough choke. Another indication of too much choke is black smoke from the exhaust pipe.
You may find after driving away that it’s helpful to momentarily pull the choke a bit when starting from a stop sign or light to keep the engine from stalling or hesitating on acceleration until it’s at normal operating temperature. If you do this, always push the knob all the way back in again as soon as you’re rolling.
If you find your engine will only run well or idle smoothly when fully warmed up with partial use of the choke, there is something wrong or out of adjustment. An engine at normal operating temperature should never need choke.
A few basic things to check in cases such as this are, first, is your engine actually at normal operating temperature? For most common collectable vehicles, normal operating temperatures range from about 160 to 200 F. These temperatures will vary depending upon environmental temperatures, driving conditions and engine load, but anything consistently below 160 degrees is not normal.
If you have just acquired the vehicle, the first thing to suspect is a former owner removed the thermostat. Keep in mind that temperature gauges may not be accurate, especially early electric gauges, so you may want to check the temperature of the radiator coolant with a thermometer.
OTHER THINGS TO CHECK
*Carburetor idle settings—are they out of adjustment?
*Vacuum leaks at the carburetor base gasket and/or the intake manifold gaskets.
*Is the carburetor tightly mounted to the intake manifold?
*Are there loose or missing plugs or fittings, and loose screws on various carburetor components?
Other possible causes are leaks in a vacuum windshield wiper system or wiper motors, a cracked intake manifold or a plug missing from the manifold. A very dirty air cleaner is another possibility, as are badly burned or out-of-adjustment ignition points or a failing ignition condenser. Water in the fuel, a failing fuel pump or a partially clogged fuel filter are other possible causes.
Last is the possibility that your carburetor needs to be cleaned or rebuilt. Many vintage carburetors have badly worn throttle butterfly bushings, which create vacuum leaks, and most repair or rebuilding kits do not include parts to fix this.
As far as rebuilding carburetors, there are far too many different types, models and variants to attempt even a basic description so buy a shop manual for your specific vehicle.
Again, the only way to have a happy relationship with your new vintage vehicle is to get to know it very well.
A GOOD RELATIONSHIP WITH AN OLD FRIEND
We have come to expect our new cars and trucks to behave like modern washing machines. We push a button and they do what they’re supposed to do without any thought or help from us. In the case of vehicles, they start instantly no matter if it’s cold or hot, raining or snowing. They shift smoothly through all their gears and steer with a fingertip on the wheel. They run quietly, and their electric windshield wipers always work. If they make any howling or whining sounds, or leak the slightest drop of fluid, there is usually something wrong.
Not so with old vehicles.
Learning how to operate your vintage car or truck may sound a bit daunting if you’ve never owned or driven a carburetor-equipped vehicle. But remember this: generations of kids grew up with such vehicles, just as they grew up without child-proof caps, safety covers on electrical outlets, bicycle helmets or car seats. You’re supposed to be smarter than us, so surely an antique vehicle can’t intimidate you!
Like old school maintenance articles? Here are a few more articles to check out.
Related: Old Cars Restoration Basics: Replacing Weatherstrip
Related: Old Cars Restoration: Bedding your brakes
Related: Old Cars Restoration: In with the good air
If you like stories like these and other classic car features, check out Old Cars magazine. CLICK HERE to subscribe.
Want a taste of Old Cars magazine first? Sign up for our weekly e-newsletter and get a FREE complimentary digital issue download of our print magazine.
