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Mazda B2200 Surges And Bucks

Q. I have a 1989 Mazda B2200. I have a stumble/surge on light throttle and deceleration. It occurs when the engine is cold and hot. I have rebuilt the carburetor, replaced plugs, fuel pump, fuel filter, air filter, tried running with the EGR valve disconnected, checked the timing and verified the advance unit works when you increase the rpm.

Mazda B2200 Surges And Bucks

Once in a while it will go several days with no surge but it always comes back. The truck accelerates fine and the mileage hasn't changed. I can't locate any vacuum leaks. The truck has 175,000 miles but the engine is still very tight and doesn't use any oil. If you are going 55 mph and slightly lift your foot, you feel the truck surge or buck and you also feel a constant surge or light stumble during steady cruising.

Any help would be appreciated, I have also verified that all the vacuum lines are properly connected.


A. What you describe is usually due to a lean air/fuel mixture. As engines get older you have to make slight adjustments to the timing and fuel mixture to compensate for wear and tear. The best way to check it is with a dwell meter. Here is how to check and adjust the fuel mixture.

Before adjusting idle speed or mixture, be sure the ignition timing, spark plugs, and carburetor float level are all in normal operating condition. Turn off all the lights and other unnecessary electrical loads. Check that all the vacuum hoses are properly routed according to the vacuum diagram.


  1. With engine already at normal operating temperature, start engine and run at 2,000 rpm for 1 minute, then let idle.
Mazda B2200 Surges And Bucks
  1. Connect a dwell meter to the A/F check connector (Br/Y wire). Set meter to 4 cylinder scale.
Mazda B2200 Surges And Bucks
  1. Check the air/fuel solenoid duty cycle (dwell) at the specified rpm (800-850 rpm). Dwell should be between 20° to 70° and varying.


Mazda B2200 Surges And Bucks
  1. Remove the carburetor and, using a small punch, drive the anti-tamper spring pin out from the bottom. Re-install the carburetor with a new base gasket
  2. Install the air cleaner and verify that the idle compensator is closed. Verify that all vacuum hoses are correctly routed.
  3. Warm up the engine and run it at idle.
  4. Connect a tachometer to the engine.
  5. Connect a dwell meter to the A/F check connector (Br/Y wire). Set meter to 4 cylinder scale.
Mazda B2200 Surges And Bucks
  1. Adjust the idle mixture screw until the air/fuel solenoid duty cycle (dwell) is varying in the preferred range, between 27° to 45°.
  2. After adjustment is completed, tap the anti-tamper spring pin back into place.

I think this will get rid of that surge.

Additional Information provided courtesy of AllDATA

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