What are the consequences of adjusting a carburetor too rich?

Adjusting a carburetor too rich means that more fuel is being delivered to the engine than is needed for proper combustion. This condition leads to incomplete burning of the fuel, which in turn increases the levels of hydrocarbons (HC) in the exhaust. Hydrocarbons are unburned or partially burned fuel compounds that are released when fuel does not burn completely due to an excess of fuel.

The consequences of running an engine with a carburetor adjusted too rich include not only higher emissions of hydrocarbons but also potential fouling of spark plugs, decreased engine efficiency, and potential buildup of carbon deposits. The combustion process is optimized when the fuel-to-air ratio is balanced, allowing for complete combustion and reducing the emissions of harmful pollutants.

In contrast, the other options do not accurately reflect what occurs with a rich carburetor setting. For instance, excessive richness would not lead to increased oxygen in the exhaust or improved fuel consumption; in fact, fuel consumption would likely increase as the engine would be using more fuel than necessary. Similarly, engine performance is often diminished rather than improved under rich conditions.