Which symptom occurs if the carburetor to manifold base plate gasket does not seal?

• A. Vacuum leak
• B. Backfire
• C. Loss of power
• D. Rough idle

Answer: (D)

A gasket that seals between the carburetor and the intake manifold blocks unmetered air from entering the engine. If that seal fails, extra air leaks in at idle, bypassing the carburetor’s metering jets. The engine then runs with a lean, unstable mixture, which makes the idle speed bounce and the engine feel rough. That uneven idle is the most direct and noticeable symptom of a base-plate gasket leak, because the idle condition relies on a precise air-fuel ratio that is disrupted by the unintended air. While a vacuum leak in general can lead to various signs, the specific, common telltale at idle from this particular leak is a rough idle.