If your Autolite 1100 carburetor hesitates when you press the throttle, it’s usually because the carburetor can’t deliver the extra fuel quickly enough to match the sudden rush of air. Here are the most common causes and what you can do to diagnose them:
1. Accelerator Pump Problems
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The accelerator pump diaphragm may be worn, stiff, or cracked, preventing a proper fuel squirt.
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If the carb has sat with ethanol fuel, the rubber often hardens and curls.
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Check by looking down the carb throat (engine off) and snapping the throttle—fuel should spray instantly.
Fix: Replace the accelerator pump with an ethanol-resistant version from Mike's Carburetor Parts.
2. Check Ball and Discharge Passage
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The discharge check ball that leads to the accelerator pump circuit may be missing, stuck, or leaking.
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If the passage is blocked, fuel can’t reach the venturi in time.
Fix: Blow through the main discharge passage, clean passages thoroughly, reseat the check ball with a light tap, and ensure the check weight is installed. The location of the check ball and check weight can be seen on this page.
3. Float Level and Fuel Supply
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A float set too low or a sticking needle/seat may starve the carb during throttle tip-in.
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Low fuel pressure from a weak pump can make hesitation worse.
Fix: Verify float height per spec (usually around 1 1/16" on the 1100) and confirm fuel pump output (about 4 PSI).
4. Vacuum Leaks
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A leak at the carb base gasket, intake manifold, or PCV system can lean out the mixture and cause hesitation.
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Spray carb cleaner around suspected areas while idling; RPM change indicates a leak.
Fix: Replace gaskets or hoses as needed.
5. Ignition Timing & Advance
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Sometimes hesitation feels like a carb issue but is caused by incorrect ignition timing or a vacuum advance problem.
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If the advance unit isn’t working, the engine won’t respond quickly to throttle.
Fix: Check base timing and verify the distributor vacuum advance is pulling in when connected.
Summary:
Most hesitation issues on the Autolite 1100 come from a weak accelerator pump, blocked pump passages, or vacuum leaks. Start with a visual check of the pump shot, then move step by step through float level, fuel delivery, and ignition.
Frequently Asked Questions
Q: How can I test if the accelerator pump on my Autolite 1100 is working?
A: With the engine off, remove the air cleaner, look down the carburetor throat, and snap the throttle. A proper accelerator pump should deliver a quick spray of fuel—if not, it indicates a pump or circuit failure.
Q: Why does the 1100 carburetor hesitate on throttle if the accelerator pump still squirts fuel?
A: Even with a working pump, hesitation may result from plugging in the accelerator pump passages or a stuck/displaced check ball, which prevents fuel from reaching the venturi at the right time.
Q: Could worn linkage or throttle shaft play a role in hesitation?
A: Yes. Worn or loose throttle shaft linkage can introduce slop, meaning the accelerator pump might not activate reliably, even if it appears functional.
Q: Are there other non-carburetor causes of hesitation I should check?
A: Definitely. Vacuum leaks, float level mis adjustment, fuel delivery restrictions, or ignition timing issues can also mimic throttle hesitation symptoms and should be ruled out.
