Which issue is NOT likely to cause high Hydrocarbons (HC) in emission tests after an engine overhaul?

High hydrocarbons (HC) in emission tests typically indicate incomplete combustion in the engine, which can be attributed to several issues that affect the air-fuel mixture or combustion process.

The correct answer points out that if a fuel filter is clogged, it would likely lead to a restriction in fuel flow rather than an excess. This restriction would typically cause the engine to run lean (not enough fuel), which usually results in reduced hydrocarbons in the exhaust because of a more complete combustion process. In contrast, if there is too much fuel or incomplete combustion, it would lead to higher HC levels.

Defective components like a thermostat, fuel pressure regulator, or valve stem seals, on the other hand, can lead to high hydrocarbons because they affect the combustion process directly, either through improper mixture composition or increased oil consumption, both of which contribute to incomplete combustion and higher hydrocarbon emissions. Therefore, the clogged fuel filter, lessening the fuel supply, is not likely to be a contributing factor to heightened HC emissions following an engine overhaul.