5 Things That Make Living with a Carburetor Easier
A properly running car is a finely tuned system of parts working in harmony. Any component, then, can make the difference between a running and driving machine and a coughing, spitting garage ornament. If one critical component is a bit persnickety, it often earns a bad reputation it may not deserve. If you know (or are) someone who’s into old cars, you probably know the love/hate affair with carburetors.
We all know the holy trinity of engine worship: Fuel, air, and spark. These three elements must exist in the right proportions for an engine to run. Because “holy quaternary” just doesn’t have the same ring to it, compression gets shoved off into the corner, to be discussed only by those who have ascended to a higher tier of diagnostics beliefs, like that guy with the long beard who is still remarkably adept at spark plug reading. He diagnosed a distributor gasket leak from across the parking lot once. I was there.
Maybe I’m misremembering, but it’s precisely that kind of guru mechanic people picture when want someone to work on their carburetor. It doesn’t take a wizard to have a great-running carbureted car, however. Just about anyone can have it. To get there and stay there takes a little bit of care, but the basics boil down to five things.
Use Clean, Non-Ethanol Fuel
Although ethanol-blended fuel does have big power potential, it is also the root of more than a few headaches for those of us with a vintage bent. Gasoline will evaporate at the temperatures most of us like to cruise in, and that means the gasoline disappears and leaves the residue of the ethanol behind. It clogs the multitude of precision passages that make a carburetor function. Most carb tuning and advice is rooted in pre-ethanol times, so even using jetting and setup advice can be tough, as ethanol fuel behaves differently compared to “pure” gasoline.
A Well-Tuned Choke
Listen to the arguments against carbs, and cold starts are oft cited as being a runaway victory for fuel injection. It’s a fair point; fuel injection has won the smooth-running game handily, but a well-tuned choke on a carb works really well considering how simple it is. After all, it carried us through when our hobby cars were simply daily drivers.
Thermostatic chokes often use a bimetallic coil, which is just two different metals bonded together that expand differently when heated or cooled. Pump the throttle once before starting the engine to set the choke, and the engine should start and set at a high idle. Consult your shop manual to get exact settings. Tuning a choke can be finicky, but when it’s all sorted, there is nothing quite like a smooth start-up on a crisp fall morning.
Happy Distributor
A professor of mine from college once told me “90 percent of your fuel problems are ignition.” People will be chasing “carb problems” for hours before realizing the damp spark plug that seems to be running too rich is actually just a plug getting weak spark or not firing at all. Keeping the ignition in top shape helps to keep many other components running smoothly—and it also assists with diagnostics for rough running.
Smooth Linkages
Binding linkages can make chokes stick and accelerator pumps function inconsistently. It’s wild to think that the carb’s exterior cleanliness is just as critical as its cleanliness inside. Road grime is attracted to oily or damp surfaces, and it only takes a small amount of oil mist from an open breather or leaky gasket to attract a surprising amount of junk, which will damage small seals or gum up finicky linkages.
Clean Air
It seems there are actually three sides to a carburetor: the fuel side, the air side, and the outside. Does that make sense? Maybe. Regardless, the air coming into an engine is the easiest pathway for all the stuff that should stay outside of an engine to get inside of it. Dirty throttle blades and intake manifolds can cause interesting problems in both carbureted and fuel-injected engines. All the delicate and small air passages that help keep carbs balanced and flowing can get clogged quickly. Keep an air filter on the intake, and your carb will be happy for a long time.
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Here in Idaho, we can buy ethanol free gas in 89 or 91. I use the 89 for all my power equipment as well as my 1979 Yamaha XS1100SF. Things start well every year, and I do not have problems with my 4 carbs on the Yamaha. I noticed by testing that ethanol fuel in small quantities will turn after less than a month! So two quarts in your lawn mower may be bad before you can use it in the spring.
Fuel Pressure–some carburetors are VERY susceptible to excessive fuel pressure. Check your car’s carb specs for proper fuel pressure indications. VW air-cooled engines/carburetors typically have very pressure- sensitive float valves. Too much pressure can over-ride the valve, over-fill the fuel bowl and result in flooding of the engine. The usual popular diagnosis is “vapor lock”–but the REAL issue is TOO MUCH fuel due to excessively high pressure output at the fuel pump.
“Gasoline will evaporate at the temperatures most of us like to cruise in, and that means the gasoline disappears and leaves the residue of the ethanol behind.”
That is a false statement. Ethanol doesn’t leave residue, it dissolves it. Almost all fuel system cleaners have ethanol as one of, if not the, primary ingredient. GASOLINE evaporates and leaves residue. So the statement is backwards.
I’ve pulled old cars from the woods or a barn and put modern gas in what looked like a clean tank. After a few hours of running, maybe after fresh gas has been in the tank a few days, the valves would sometimes start sticking. It’s from a varnish-like residue left on the valves from the residue in the tank left from old gas evaporating. I’ve drained old gas from a tank then put in fresh with the same results. I haven’t done this in 20 years, but a few people I know have pulled cars out of hibernation over the last 2-3 years, where the car has sat for as little as two years, a couple over 10, with the same results. I always recommend pulling the tank if a car has sat for a long time and cleaning thoroughly before using, especially if more than five years. Some have been ok in the 1-5 year range.
The very basic with any carburetor using any fuel is clean fuel. Many systems only use the tiny sintered bronze filter located right at the bowl inlet.
We can take a hint by looking at FI systems, which typically use a large inline filter (paper or fiber element) somewhere between the tank and the carburetor.
My 77 vette had a Mallory distributor and holly 600 on stock block with vortec heads when I bought it in 2014. It had the external coil as well. Always had a hard time getting it to run properly at lower rpm’s. The original intake had been replaced with a performer. It got to where it would just die crusing at 35 mph but would start back up until one day at the gas pumps no start. Triple A time so a parts guy said why don’t you go back to factory set up, so I did it with Delco distributor wires plugs a quadrajet and I took electric choke off of Holly and made it work on new carburetor and timed it by ear. Long story short choke works great she runs smooth.
Ugggghhh, fuel systems,
I will be replacing the in tank fuel pump in my 88 dodge Daytona for the 5th time. Pumps seize up after a few years sitting submerged in ethanol mixed gas.
On this earlier fuel injected car,
It rots the fuel lines, eats the MPI injector and rusts out the tank.
Switching gears (no pun intended) PCV valves, it’s a three dollar part that can mess up your whole engine performance,
Don’t question a $3 part, just replace it.
As far as chokes go, there is a small tunnel in the manifold, runs under the carburetor. hot exhaust from one side of the inner intake to the other side, it heats up the choke coil, if it plugs up (and they all eventually do) your choke stays cold, engine floods/stalls out until the engine is warm.
It’s not an easy fix since removal of the intake is required, and burrowing out the carbon.
Seems like every Ford, Dodge and Pontiac I’ve owned need a clearing
In urban Northern California ethanol free gasoline is very, very rare. I have used the regular issue 10% ethanol gasoline in old motorcycles and scooters for years, and some have sat unused for months and months, and still no problems with the fuel. As others have said, ethanol is a good solvent that removes the shellac-like stuff that stays after gasoline ages and dries up. If the fuel system isn’t clean you’ll have problems with that stuff clogging up filters and carbs. I use E-85, 85% ethanol, to soak clean old filthy gas tanks. Just dump the old gas, put in the E85, cap it, slosh it around every few hours for a couple of days and then pour it out, quickly, and take both jugs of fuel to a recycling station. Meanwhile either re-fill the tank with gas or fog it inside to stop surface rust.
Yes, I had a 78 RT with a 318. The crossover in the manifold would fowl up and the carb would get cold and close the choke. Many times I had to put a piece of cardboard in to keep the choke plate open in order to get home. I found that by removing the EGR you could push a 3/8” drain snake through there and ream it out.
Saved a lot of effort removing the intake.
For the shade tree. – Give the outside of the carb on vehicle or face a good spray down with tune up in a can top to bottom before cracking it open to prevent keep nasty bits from finding there way inside. Make sure to hit to hit any unseen surfaces well. – Place elevated in cheap disposable aluminum roasting tray and repeat. – Have that old clean cupcake tray on hand to keep parts in order, prevent runaways and make sure nothing gets left behind- Be prepared to deal with ‘ why did they make this damn clip so small’. Do not loose damn clip.- Reinstall basic rebuilt carburetor. – Tune as required in small increments- Happy motoring
Once again the “ethanol” bogeyman is dragged out. Use “ethanol free” gasoline advise is incorrect and is useless in most parts of the country. Fact is once ethyl lead additives were removed from gasoline a change in refining was required to increase octane which results in gasoline that is more volatile (evaporates faster). There is also the incorrect statement ethanol brings water into gasoline that is NOT true. In fact it absorbs some of the water that accumulates. Those who fly airplanes know to drain the tank sumps of water BEFORE each first flight of the day AND THERE IS NO ETHANOL in small airplane engine fuel!!!!! Water in the air will condense on the surface of gasoline as it evaporates and COOLS. Finally pure ethanol does NOT CORRODE carburetors. By law industrial ethanol has to be “denatured” so folks will not drink it. Some ethanol producers leave refinement impurities in the ethanol that can be corrosive so it qualifies for vehicle fuel additive. This is the issue, but not all do it A buddy with a pristine 1938 Packard worked himself into a panic due all the ETHANOL misinformation. There is NO ethanol free fuel in his area. He removed the Packard engine carburetor and it was SPOTLESS, no deposits, no corrosion!!! He put it back together and never worried again.
Common Kyle, do your homework.
Thanks for the tip Frank. Note too that many Marina’s sell 100 plus octanes for race boats. A bit pricey but they are leaded. I love that smell of leaded fuel exiting an exhaust!
I didn’t say this before, but as many of you already know Ethanol is alcohol and other chemicals mandated by the Government and Alcohol turns your gas tank into a slurry of dirt, water, impurities etc. [the more humid it is the more water condensates inside your gas tank] It’s all just floating around in there, stimulated by the properties of the alcohol…. clean new fuel filters are a must. Gasoline in the tank allows the dirt, impurities and water to settle to the bottom. Big difference in the corrosion, gummed up fuel system and erratic performance of any carburater. If anyone has been using Ethanol in a carburated engine, I recommend dropping the gas tank, have it cleaned out, replace any steel fuel lines, clean out the fuel pump, have your carb guy pull it out and clean and replace corroded parts. Then use REC 90 [short for recreational 90 octane].
I drove my 65 Corvette, Carter 4 barrel carb, to the Boston Aston Martin dealership to look at a V8 Vantage. Something was banging under the hood. The service manager comes out front, looks at and says your fuel pump is loose. Bring her around back and we’ll tighten it up. I get the car in there and all the techs put down their tools to look at the car. Here we are in the shop with many cars worth tons of money, and they all want to look at the coupe. A young mechanic leans in toward the engine and says with wonder, “Is that a carburetor?” It was like the kid had just seen a dinosaur or Big Foot. Great people at Aston Martin of Boston. Everyone was terrific and they would not accept payment for fixing my little red baby. I love the sound and feel of that 4 barrel kicking in when you boot it. I can still see the look on the young mechanic’s face and the sound of wonderment in his voice when he said, “Is that a carburetor?”
“I never joke about my work, 007.”
I owned a 1951 Mercury Pickup with a flathead in it. Over 40 years ago I plumbed a 6 volt electric fuel pump into the same line as the mechanical pump. When it sat for weeks I would use the electric fuel pump to pump the gas into the carburetor and then shut it off. It would fire right up. Where I winter stored it the guy would comment that truck was the best staring vehicle of all the vehicles he had wintered stored. I now do it to all my carbureted vehicles!!
I have a 66′ Vette with the original 327 and a 600 Holly Carb. It ran for years very well until ethanol started giving me Vaporlock! I have read that installing a electric fuel pump at the tank will raise the presure above the vapor point of the fuel and prevent vapor lock. If anyone has experience with this please let me know.
It only helps the fuel in the lines avoid vapor bubbles, when the fuel gets to the carb it will still vapor lock
Another problem with fuel is that we don’t have all the facts readily available. My modified ’79 Corvette engine (with Holley 750) ran great in Michigan on Mobil with ethanol 93 octane. Had it transported to Florida. It ran great until I had to refuel (also 93 octane Mobil with ethanol). Then it started vapor locking. As more and more FL fuel was introduced the range got shorter and shorter before vapor lock put me on the side of the road until things cooled off. Eventually I could only get about 5 trouble free miles away from home. This never happened in Michigan. I tried everything (needle and seat adjustments, mixture changes, new gaskets, jet changes, different Holley that was known to work well and also changed to an electric fuel pump). The real problem: The blend of FL fuel is different (Reed Vapor Pressure) than MI. To solve the problem, I ditched the mechanical pump, installed an electric fuel pump and fabricated a “return” system with a regulator. I had to drop the tank and add a port for the return line. That stopped the vapor lock, but not exactly a simple fix. Terrible.