If your vehicle was made in the past 20 years or so, you’ve probably heard of carburetors, but never really dealt with one. For personal vehicles at least, they’ve fallen out of favor for newer and more reliable technology. But they can still be found on classic cars, hot rods, some motorcycles and even lawn mowers … and if you have one, you may have noticed how the cold affects carburetors and wondered why. Well, this one’s for you.
Carburetors are responsible for mixing the exact amount of air and fuel necessary for combustion and delivering it to the engine. They rely on engine vacuum to pull in air from outside and fuel through small jets (so it can be easily vaporized) in the correct blend. Then they make sure that just enough of the mixture gets into the engine under changing conditions. Too much fuel and the mixture is too rich – you waste fuel and run the risk of flooding the engine. Too much air and it’s lean – you lose performance and may stall out. Carburetors are mechanical in nature and can be finicky. Modern fuel injection is electronic, more precise and dependable.
A Breath of Cold Air
Carburetors have an internal hourglass shape. Even in not-so-cold weather around 50 degrees, there is a tendency for the carburetor to cool the air as it passes rapidly through the narrow passage of this shape, freezing any condensation that may have crept in. The condensation problem arises in freezing conditions, too. Though it might not be much, fuel lines can accumulate small amounts of water over time and moisture can fall into the carburetor itself. Considering the small diameter of the fuel jets and fuel lines, it doesn’t take much ice to block them.
Then the main culprit: cold air. Cold air is denser than warm air, which means even a properly tuned carburetor may struggle with a too-lean mixture on a cold morning as it pulls in the same volume of air, but more tightly packed, increasing the air-to-fuel ratio. When cold, the fuel coming out of the jets doesn’t vaporize as well, which leads to an improper combination.
The thing a cold carb needs the most is warmth. If you can park inside or under something, that’s a start, but otherwise let the engine warm up for a good few minutes before you get on the road.
If your vehicle isn’t even starting in the first place, remove the air filter on top of the carburetor and take a peek inside. If the choke plate is more vertical than horizontal, it might need a slight adjustment in the colder months (turn it more horizontal) so that the initial air intake is a little more restricted, making the mixture richer. But be warned: Tuning a carburetor is a real skill, so it’s best to consult a professional if you’re new to it. If you’re in a real pinch, you can spray a little starter fluid over the choke, but don’t rely too heavily on this, as extended use will damage your engine.
Beyond warmth, keep your fuel lines and jets clean with a fuel additive and change your fuel filter when necessary. Staying on top of routine maintenance generally also enables your engine and battery to do their part to get you where you need to go.
Check out all the fuel & emission system parts
Photos courtesy of Blair Lampe.
Blair Lampe is a New York-based professional mechanic, blogger, theater technician, and speechwriter. In her downtime she enjoys backpacking wherever her boots will carry her, rock climbing, experimental theatre, a crisp rosé , and showering love on her 2001 Sierra truck.