What condition would cause hesitation when the throttle is rapidly advanced from idle to full power in an engine using a float carburetor?

What condition would cause hesitation when the throttle is rapidly advanced from idle to full power in an engine using a float carburetor?

• A. Lean fuel mixture
• B. Vacuum leak
• C. Malfunctioning accelerator pump
• D. Worn spark plugs

Answer: (C)

When you snap the throttle from idle to full power in a float carburetor, the engine expects a rapid increase in both air and fuel. The accelerator pump provides a short burst of extra fuel exactly at that moment to prevent the mixture from going too lean. If the accelerator pump isn’t delivering that boost—due to a faulty diaphragm, a clogged discharge, or the pump not firing—the engine runs lean during the transition and hesitates or stumbles until the air-fuel mixture catches up. That specific hesitation at throttle tip-in is a classic sign that the accelerator pump isn’t functioning properly. Other issues like a generally lean mixture, a vacuum leak, or worn spark plugs can cause rough running, but they don’t explain the distinct stumble that occurs specifically when rapidly advancing the throttle.

When you snap the throttle from idle to full power in a float carburetor, the engine expects a rapid increase in both air and fuel. The accelerator pump provides a short burst of extra fuel exactly at that moment to prevent the mixture from going too lean. If the accelerator pump isn’t delivering that boost—due to a faulty diaphragm, a clogged discharge, or the pump not firing—the engine runs lean during the transition and hesitates or stumbles until the air-fuel mixture catches up. That specific hesitation at throttle tip-in is a classic sign that the accelerator pump isn’t functioning properly. Other issues like a generally lean mixture, a vacuum leak, or worn spark plugs can cause rough running, but they don’t explain the distinct stumble that occurs specifically when rapidly advancing the throttle.