Over time and miles, your car might start to slow down. It might not accelerate as quickly as it once did; the engine may not run as smoothly as you remember, or the fuel economy may dip—but ...

Here’s how you started a car with a carburetor on a cold morning back in the “good old days.” You’d pull out the choke, pump the throttle a few times, and turn the key. If you didn’t overdo it and ...