Which of the following is an example of tampering with emission controls?

Tampering with emission controls generally refers to actions that interfere with the mechanisms designed to reduce harmful emissions from vehicles. In this instance, the failure to install limiter caps after servicing the carburetor is a clear example of such tampering. The limiter caps are crucial components that help regulate the air-fuel mixture and, therefore, play a significant role in controlling emissions. By neglecting to install them, there's a deliberate act of compromising the vehicle's emission control system, which can lead to increased emissions beyond allowable limits.

In contrast, using high-quality lubricants, proper installation of emission systems, and regular maintenance of the vehicle all contribute positively to the efficiency and effectiveness of emission controls. These actions help to ensure that the vehicle meets regulatory standards regarding emissions, thereby demonstrating responsible vehicle management rather than tampering.