Weber Marine Hesitates When Throttling Up

Weber Marine Carburetor Hesitation and Bogging

Causes, Diagnosis, and Accelerator Pump Testing

If your Weber marine carburetor hesitates, bogs down, or stalls when you open the throttle, the issue is usually related to the accelerator pump circuit. In some cases, improper ignition or distributor advance can create similar symptoms, but the carburetor should be checked first.

Common Symptoms of Weber Marine Carburetor Hesitation

• Engine bogs or dies when throttle is applied

• Hesitation when accelerating from idle

• Engine runs fine at idle but stumbles under load

• Delayed throttle response

These symptoms almost always point to a lack of fuel delivery during throttle transition.

Step 1: Check Accelerator Pump Discharge

With the engine off and the flame arrestor removed:

1. Look straight down into the carburetor throat

2. Open the throttle by hand

3. You should see two strong, immediate fuel squirts from the accelerator pump discharge

If fuel does not squirt, or only dribbles, there is a blockage or leak in the accelerator pump circuit.

Step 2: Bench Test the Accelerator Pump Circuit

This test is best done with the carburetor removed.

1. Remove the carburetor top

2. Fill the float bowl with mineral spirits (safer than gasoline for testing)

3. With the accelerator pump fully down, slowly pull it upward

What to Look For:

• The pump well should fill with fuel

• If it does not fill, check the check ball at the bottom of the pump well

• Some Weber marine carburetors feed the pump well through a side slot, so verify that passage is clear

A stuck or blocked check ball will prevent the pump from charging with fuel.

Step 3: Verify Pump-to-Discharge Passage

Once the pump well is full:

1. Press the accelerator pump downward

2. Fuel should exit the main discharge port

If no fuel appears:

• Spray carburetor cleaner through the pump well passage leading to the discharge

• Blow compressed air through the passage

• This passage is commonly clogged by varnish or debris

Step 4: Check the Main Discharge Check Valve

The main discharge assembly typically contains:

• A check weight, or

• A check ball and weight

To test it:

1. Hold the check weight or ball firmly down

2. Press the accelerator pump

Correct Behavior:

• You should feel resistance

• Fuel should not leak back upward

If fuel leaks past the check ball:

• Lightly tap the check ball to help it reseat

• A leaking check valve will cause hesitation even if the pump is working

Step 5: Final Verification

After reassembly:

1. Reinstall the main discharge cover

2. Operate the throttle by hand

3. Confirm two strong, clean fuel squirts from the discharge

If the squirts are immediate and consistent, the accelerator pump circuit is functioning correctly.

Other Possible Causes of Hesitation

If the accelerator pump checks out, also inspect:

• Distributor advance operation

• Vacuum leaks

• Incorrect pump stroke adjustment

• Warped carburetor top causing internal leaks

Summary

Most Weber marine carburetor hesitation problems are caused by:

• Blocked accelerator pump passages

• Stuck or leaking check balls

• Weak or uncharged pump wells

• Leaking main discharge check valves