Disadvantages of Leaving a Carburetor Choke Wide Open All the Time on a 302 Ford Engine

Written by wade shaddy
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Disadvantages of Leaving a Carburetor Choke Wide Open All the Time on a 302 Ford Engine
Running your car on full choke is environmentally unsound. (Jupiterimages/Comstock/Getty Images)

Most cars built before 1970 had manual chokes operated by a lever on your dash. You could pull the lever out until the car warmed up and then shut it, or you could leave it out all the time if the engine ran better that way. There are still plenty of Ford 302 engines out there with manual chokes, but leaving them on full choke can cause problems

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Fuel Economy

When the choke is on full, it pours gas into the carburettor at almost twice the volume. The cylinders burn what they need and the rest of the gas goes out the tailpipe as vapour. This is extremely wasteful and will cause your gas mileage to decrease by half or more. If your 302 is rated at 20mpg, you will get less than 10mpg if you run it with the choke on full.

Poor Acceleration and Stalling

The 302 is designed to accelerate at a given fuel flow rate; spark plug firing advances as more gas is introduced into the cylinder. When the choke is full, gas is dumped into the cylinder, causing the engine to misfire due to saturated spark plugs. The engine will buck and miss, catching and spinning the tires only to choke and stall. You may not be able to get the engine started again until the gas dries off the electrodes on the plugs.

Fouling Spark Plugs

Fouled spark plugs are a direct cause of running the engine with full choke. When gas burns, it creates a small amount of black residue called varnish. The varnish builds up on the electrodes, preventing them from firing. When this happens, your car will miss and the spark plugs will need to be removed and cleaned or changed. Fouled spark plugs from running an engine on open choke is common.


A Ford 302 engine can only burn a given amount of gas each time a cylinder fires. When you run the engine on full choke, the motor burns as much of the gas as it can and the rest is expelled out in raw gas vapour. This is characterised by black smoke coming from the car's exhaust. Black smoke contains pollutants that dirty the environment and cars that smoke are illegal in most states. Pollution is probably the single most devastating effect from running a Ford 302 engine with the choke wide open.

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