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Carburetor Problems


Although most automotive engines no longer use a carburetor, having moved to fuel injection, they are still common on older vehicles, smaller engines such as motorcycles, and on household yard and garden tools. So they are still relevant to repair subjects and are something many DIY mechanics are likely to deal with.

A carb can have many problems associated with it, though few things are actually the carburetor's fault - often the symptom is assumed to be the carb when it is actually something related instead.

How a Carburetor Works

The carb is a relatively simple mechanical device that controls the fuel-air mixture entering the cylinders based on throttle position.

Most carburetors use direct input from the driver (via the accelerator and possibly choke) to control this mixture, which in turn controls the engine's performance.

Control is through a choke, which is usually a levered plate that opens and closes to allow air into the carb, and a float chamber/jet(s) which control fuel flow. The carburetor jets the fuel into the air as it enters the cylinder, creating the combustible mix that fires the engine.

Common Symptoms and Solutions

The three most common problems with a carburetor are:

  1. Lean Mixture
  2. Rich Mixture
  3. Incorrect Adjustment

A lean mixture is when there is too much air in the fuel-air mix, causing cylinders to not burn with enough pressure to move at optimum efficiency.

A rich mixture is the opposite, with too much fuel or not enough air, causing cylinders to not burn all of the fuel injected and become inefficient.

Incorrect adjustments are when other adjustments on the carb, such as the size of the fuel jet or the position of the air intake, are wrong. This causes lean or rich mixtures or it can cause fouling, allowing foreign objects or soot into the mix.

Carburetors require regular maintenance. They should be cleaned with every oil change using a fuel additive or with a formula directly sprayed into the carburetor itself. This keeps carbon from building up and fouling the carb's performance. Springs, adjustments, and moving parts on the carburetor should be inspected annually when a vehicle tuneup is done - some springs and moving parts can wear with time or move out of adjustment.

Examine all idle and main mixture adjustments (refer to your owner's manual) and check O-rings on fittings to be sure they are not cracked or damaged. Adjusting the screws for this purpose can tune the carb to the vehicle's needs.

On any engine with a carburetor, regular maintenance and preventive work can ensure lifelong service.